From: Jim Cromie <jim.cromie@gmail.com>
Move the JUMP_LABEL to the top of the struct, since theyre both
align(8) and this closes a pahole (unfortunately trading for padding,
but still).
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
---
include/linux/dynamic_debug.h | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
index 497130816e9c..b9237e4ecd1b 100644
--- a/include/linux/dynamic_debug.h
+++ b/include/linux/dynamic_debug.h
@@ -14,6 +14,12 @@
* the special section is treated as an array of these.
*/
struct _ddebug {
+#ifdef CONFIG_JUMP_LABEL
+ union {
+ struct static_key_true dd_key_true;
+ struct static_key_false dd_key_false;
+ } key;
+#endif
/*
* These fields are used to drive the user interface
* for selecting and displaying debug callsites.
@@ -53,12 +59,6 @@ struct _ddebug {
#define _DPRINTK_FLAGS_DEFAULT 0
#endif
unsigned int flags:8;
-#ifdef CONFIG_JUMP_LABEL
- union {
- struct static_key_true dd_key_true;
- struct static_key_false dd_key_false;
- } key;
-#endif
} __attribute__((aligned(8)));
enum class_map_type {
--
2.42.0.869.gea05f2083d-googOn Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
>
> From: Jim Cromie <jim.cromie@gmail.com>
>
> Move the JUMP_LABEL to the top of the struct, since theyre both
> align(8) and this closes a pahole (unfortunately trading for padding,
> but still).
>
> Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
let me add, I havent really tested this, nevermind thorough.
specifically, I didnt look for any offset dependence on the static-key
inside their container.
Conversely, maybe theres a free default or something in there.
> ---
> include/linux/dynamic_debug.h | 12 ++++++------
> 1 file changed, 6 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> index 497130816e9c..b9237e4ecd1b 100644
> --- a/include/linux/dynamic_debug.h
> +++ b/include/linux/dynamic_debug.h
> @@ -14,6 +14,12 @@
> * the special section is treated as an array of these.
> */
> struct _ddebug {
> +#ifdef CONFIG_JUMP_LABEL
> + union {
> + struct static_key_true dd_key_true;
> + struct static_key_false dd_key_false;
> + } key;
> +#endif
> /*
> * These fields are used to drive the user interface
> * for selecting and displaying debug callsites.
> @@ -53,12 +59,6 @@ struct _ddebug {
> #define _DPRINTK_FLAGS_DEFAULT 0
> #endif
> unsigned int flags:8;
> -#ifdef CONFIG_JUMP_LABEL
> - union {
> - struct static_key_true dd_key_true;
> - struct static_key_false dd_key_false;
> - } key;
> -#endif
> } __attribute__((aligned(8)));
>
> enum class_map_type {
> --
> 2.42.0.869.gea05f2083d-goog
>
sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
>
> On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> >
> > From: Jim Cromie <jim.cromie@gmail.com>
> >
> > Move the JUMP_LABEL to the top of the struct, since theyre both
> > align(8) and this closes a pahole (unfortunately trading for padding,
> > but still).
> >
> > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
>
> let me add, I havent really tested this, nevermind thorough.
> specifically, I didnt look for any offset dependence on the static-key
> inside their container.
> Conversely, maybe theres a free default or something in there.
>
Any idea how to properly test the relocation of the key ?
> > ---
> > include/linux/dynamic_debug.h | 12 ++++++------
> > 1 file changed, 6 insertions(+), 6 deletions(-)
> >
> > diff --git a/include/linux/dynamic_debug.h b/include/linux/dynamic_debug.h
> > index 497130816e9c..b9237e4ecd1b 100644
> > --- a/include/linux/dynamic_debug.h
> > +++ b/include/linux/dynamic_debug.h
> > @@ -14,6 +14,12 @@
> > * the special section is treated as an array of these.
> > */
> > struct _ddebug {
> > +#ifdef CONFIG_JUMP_LABEL
> > + union {
> > + struct static_key_true dd_key_true;
> > + struct static_key_false dd_key_false;
> > + } key;
> > +#endif
> > /*
> > * These fields are used to drive the user interface
> > * for selecting and displaying debug callsites.
> > @@ -53,12 +59,6 @@ struct _ddebug {
> > #define _DPRINTK_FLAGS_DEFAULT 0
> > #endif
> > unsigned int flags:8;
> > -#ifdef CONFIG_JUMP_LABEL
> > - union {
> > - struct static_key_true dd_key_true;
> > - struct static_key_false dd_key_false;
> > - } key;
> > -#endif
> > } __attribute__((aligned(8)));
> >
> > enum class_map_type {
> > --
> > 2.42.0.869.gea05f2083d-goog
> >
On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@semihalf.com> wrote:
>
> sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
> >
> > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > >
> > > From: Jim Cromie <jim.cromie@gmail.com>
> > >
> > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > but still).
> > >
> > > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> >
> > let me add, I havent really tested this, nevermind thorough.
> > specifically, I didnt look for any offset dependence on the static-key
> > inside their container.
> > Conversely, maybe theres a free default or something in there.
> >
>
> Any idea how to properly test the relocation of the key ?
I was hoping Jason knew it from memory.
I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.
I just checked `pahole vmlinux` output for the existence of 0-offset keys.
Its not conclusive, cuz im only looking at x86.
it does occur, but only for "sub-types".
struct static_key_true {
struct static_key key; /* 0 16 */
/* size: 16, cachelines: 1, members: 1 */
/* last cacheline: 16 bytes */
};
struct static_key_false {
struct static_key key; /* 0 16 */
/* size: 16, cachelines: 1, members: 1 */
/* last cacheline: 16 bytes */
};
struct static_key_false_deferred {
struct static_key_false key; /* 0 16 */
...};
struct static_key_mod {
struct static_key_mod * next; /* 0 8 */
...};
struct static_key_deferred {
struct static_key key; /* 0 16 */
pt., 10 lis 2023 o 22:01 <jim.cromie@gmail.com> napisał(a):
>
> On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> >
> > sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
> > >
> > > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > >
> > > > From: Jim Cromie <jim.cromie@gmail.com>
> > > >
> > > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > > but still).
> > > >
> > > > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> > >
> > > let me add, I havent really tested this, nevermind thorough.
> > > specifically, I didnt look for any offset dependence on the static-key
> > > inside their container.
> > > Conversely, maybe theres a free default or something in there.
> > >
> >
> > Any idea how to properly test the relocation of the key ?
>
> I was hoping Jason knew it from memory.
>
> I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.
>
> I just checked `pahole vmlinux` output for the existence of 0-offset keys.
> Its not conclusive, cuz im only looking at x86.
>
> it does occur, but only for "sub-types".
>
> struct static_key_true {
> struct static_key key; /* 0 16 */
>
> /* size: 16, cachelines: 1, members: 1 */
> /* last cacheline: 16 bytes */
> };
> struct static_key_false {
> struct static_key key; /* 0 16 */
>
> /* size: 16, cachelines: 1, members: 1 */
> /* last cacheline: 16 bytes */
> };
> struct static_key_false_deferred {
> struct static_key_false key; /* 0 16 */
> ...};
> struct static_key_mod {
> struct static_key_mod * next; /* 0 8 */
> ...};
> struct static_key_deferred {
> struct static_key key; /* 0 16 */
I will test it on arm64.
niedz., 12 lis 2023 o 17:28 Łukasz Bartosik <lb@semihalf.com> napisał(a):
>
> pt., 10 lis 2023 o 22:01 <jim.cromie@gmail.com> napisał(a):
> >
> > On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > >
> > > sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
> > > >
> > > > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > > >
> > > > > From: Jim Cromie <jim.cromie@gmail.com>
> > > > >
> > > > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > > > but still).
> > > > >
> > > > > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> > > >
> > > > let me add, I havent really tested this, nevermind thorough.
> > > > specifically, I didnt look for any offset dependence on the static-key
> > > > inside their container.
> > > > Conversely, maybe theres a free default or something in there.
> > > >
> > >
> > > Any idea how to properly test the relocation of the key ?
> >
> > I was hoping Jason knew it from memory.
> >
> > I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.
> >
> > I just checked `pahole vmlinux` output for the existence of 0-offset keys.
> > Its not conclusive, cuz im only looking at x86.
> >
> > it does occur, but only for "sub-types".
> >
> > struct static_key_true {
> > struct static_key key; /* 0 16 */
> >
> > /* size: 16, cachelines: 1, members: 1 */
> > /* last cacheline: 16 bytes */
> > };
> > struct static_key_false {
> > struct static_key key; /* 0 16 */
> >
> > /* size: 16, cachelines: 1, members: 1 */
> > /* last cacheline: 16 bytes */
> > };
> > struct static_key_false_deferred {
> > struct static_key_false key; /* 0 16 */
> > ...};
> > struct static_key_mod {
> > struct static_key_mod * next; /* 0 8 */
> > ...};
> > struct static_key_deferred {
> > struct static_key key; /* 0 16 */
>
> I will test it on arm64.
Hi Jim,
I verified that relocation of JUMP_LABEL to the top of the _ddebug
struct does not brak dynamic debug functionality on arm64.
I double checked I had CONFIG_JUMP_LABEL enabled in the kernel config for arm64.
I was able to enable/disable callsites and see debug logs being written.
But if you're concerned there might be issue related to that
relocation on other architectures then let's drop this patch
and I will use pahole instead of padding for location of flags and
trace destination fields.
What do you think ?
Thanks,
Lukasz
On Fri, Nov 24, 2023 at 7:39 AM Łukasz Bartosik <lb@semihalf.com> wrote:
>
> niedz., 12 lis 2023 o 17:28 Łukasz Bartosik <lb@semihalf.com> napisał(a):
> >
> > pt., 10 lis 2023 o 22:01 <jim.cromie@gmail.com> napisał(a):
> > >
> > > On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > >
> > > > sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
> > > > >
> > > > > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > > > >
> > > > > > From: Jim Cromie <jim.cromie@gmail.com>
> > > > > >
> > > > > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > > > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > > > > but still).
> > > > > >
> > > > > > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> > > > >
> > > > > let me add, I havent really tested this, nevermind thorough.
> > > > > specifically, I didnt look for any offset dependence on the static-key
> > > > > inside their container.
> > > > > Conversely, maybe theres a free default or something in there.
> > > > >
> > > >
> > > > Any idea how to properly test the relocation of the key ?
> > >
> > > I was hoping Jason knew it from memory.
> > >
> > > I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.
> > >
> > > I just checked `pahole vmlinux` output for the existence of 0-offset keys.
> > > Its not conclusive, cuz im only looking at x86.
> > >
> > > it does occur, but only for "sub-types".
> > >
> > > struct static_key_true {
> > > struct static_key key; /* 0 16 */
> > >
> > > /* size: 16, cachelines: 1, members: 1 */
> > > /* last cacheline: 16 bytes */
> > > };
> > > struct static_key_false {
> > > struct static_key key; /* 0 16 */
> > >
> > > /* size: 16, cachelines: 1, members: 1 */
> > > /* last cacheline: 16 bytes */
> > > };
> > > struct static_key_false_deferred {
> > > struct static_key_false key; /* 0 16 */
> > > ...};
> > > struct static_key_mod {
> > > struct static_key_mod * next; /* 0 8 */
> > > ...};
> > > struct static_key_deferred {
> > > struct static_key key; /* 0 16 */
> >
> > I will test it on arm64.
>
> Hi Jim,
>
> I verified that relocation of JUMP_LABEL to the top of the _ddebug
> struct does not brak dynamic debug functionality on arm64.
> I double checked I had CONFIG_JUMP_LABEL enabled in the kernel config for arm64.
> I was able to enable/disable callsites and see debug logs being written.
>
> But if you're concerned there might be issue related to that
> relocation on other architectures then let's drop this patch
> and I will use pahole instead of padding for location of flags and
> trace destination fields.
> What do you think ?
>
On balance, I think it should go in.
0 - my bias was towards abundance of paranoia
1 - youve done real work to evaluate the actual risk
2 - Jason is on thread, hasnt said WHOA
3 - actual patches have seen some testing (lkp-robot included)
4 - static-keys/jump-labels have been around a long time
One new topic:
Do you have any thoughts or plans wrt self-testing ?
the addition of private instances,
that can be opened & closed, and written to by +T:private_1
would benefit greatly from a test harness to validate it.
so far all Ive done is demo scripts
:-) thanks
> Thanks,
> Lukasz
niedz., 26 lis 2023 o 07:00 <jim.cromie@gmail.com> napisał(a):
>
> On Fri, Nov 24, 2023 at 7:39 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> >
> > niedz., 12 lis 2023 o 17:28 Łukasz Bartosik <lb@semihalf.com> napisał(a):
> > >
> > > pt., 10 lis 2023 o 22:01 <jim.cromie@gmail.com> napisał(a):
> > > >
> > > > On Fri, Nov 10, 2023 at 7:51 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > > >
> > > > > sob., 4 lis 2023 o 02:49 <jim.cromie@gmail.com> napisał(a):
> > > > > >
> > > > > > On Fri, Nov 3, 2023 at 7:10 AM Łukasz Bartosik <lb@semihalf.com> wrote:
> > > > > > >
> > > > > > > From: Jim Cromie <jim.cromie@gmail.com>
> > > > > > >
> > > > > > > Move the JUMP_LABEL to the top of the struct, since theyre both
> > > > > > > align(8) and this closes a pahole (unfortunately trading for padding,
> > > > > > > but still).
> > > > > > >
> > > > > > > Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
> > > > > >
> > > > > > let me add, I havent really tested this, nevermind thorough.
> > > > > > specifically, I didnt look for any offset dependence on the static-key
> > > > > > inside their container.
> > > > > > Conversely, maybe theres a free default or something in there.
> > > > > >
> > > > >
> > > > > Any idea how to properly test the relocation of the key ?
> > > >
> > > > I was hoping Jason knew it from memory.
> > > >
> > > > I have booted dd-kitchen-sink, which includes it, and it didnt melt the box.
> > > >
> > > > I just checked `pahole vmlinux` output for the existence of 0-offset keys.
> > > > Its not conclusive, cuz im only looking at x86.
> > > >
> > > > it does occur, but only for "sub-types".
> > > >
> > > > struct static_key_true {
> > > > struct static_key key; /* 0 16 */
> > > >
> > > > /* size: 16, cachelines: 1, members: 1 */
> > > > /* last cacheline: 16 bytes */
> > > > };
> > > > struct static_key_false {
> > > > struct static_key key; /* 0 16 */
> > > >
> > > > /* size: 16, cachelines: 1, members: 1 */
> > > > /* last cacheline: 16 bytes */
> > > > };
> > > > struct static_key_false_deferred {
> > > > struct static_key_false key; /* 0 16 */
> > > > ...};
> > > > struct static_key_mod {
> > > > struct static_key_mod * next; /* 0 8 */
> > > > ...};
> > > > struct static_key_deferred {
> > > > struct static_key key; /* 0 16 */
> > >
> > > I will test it on arm64.
> >
> > Hi Jim,
> >
> > I verified that relocation of JUMP_LABEL to the top of the _ddebug
> > struct does not brak dynamic debug functionality on arm64.
> > I double checked I had CONFIG_JUMP_LABEL enabled in the kernel config for arm64.
> > I was able to enable/disable callsites and see debug logs being written.
> >
> > But if you're concerned there might be issue related to that
> > relocation on other architectures then let's drop this patch
> > and I will use pahole instead of padding for location of flags and
> > trace destination fields.
> > What do you think ?
> >
>
>
> On balance, I think it should go in.
> 0 - my bias was towards abundance of paranoia
> 1 - youve done real work to evaluate the actual risk
> 2 - Jason is on thread, hasnt said WHOA
> 3 - actual patches have seen some testing (lkp-robot included)
> 4 - static-keys/jump-labels have been around a long time
>
> One new topic:
>
> Do you have any thoughts or plans wrt self-testing ?
>
Actually I didn't think about it at all ;). It is not so common
practice to write tests among kernel developers. Addition of trace
instances & events to the dynamic debug is a major change so I see the
value in having it thoroughly tested. That said I'm not saying no to
writing test harness for that purpose but I wonder if there is any
test framework in the kernel that could be reused or is everyone on
their own when it comes to the testing area ?
Thanks,
Lukasz
> the addition of private instances,
> that can be opened & closed, and written to by +T:private_1
>
> would benefit greatly from a test harness to validate it.
> so far all Ive done is demo scripts
>
> :-) thanks
>
> > Thanks,
> > Lukasz
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