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[PATCH] dm-verity: Remove WQ_UNBOUND.

Nathan Huckleberry posted 1 patch 2 years, 7 months ago 
drivers/md/dm-verity-target.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
[PATCH] dm-verity: Remove WQ_UNBOUND.
Posted by Nathan Huckleberry 2 years, 7 months ago 
Setting WQ_UNBOUND increases scheduler latency on ARM64.  This is likely
due to the asymmetric architecture of ARM64 processors.

I've been unable to reproduce the results that claim WQ_UNBOUND gives a
performance boost on x86-64.

This flag is causing performance issues for multiple subsystems within
Android.  Notably, the same slowdown exists for decompression with
EROFS.

| open-prebuilt-camera  | WQ_UNBOUND | ~WQ_UNBOUND   |
|-----------------------|------------|---------------|
| verity wait time (us) | 11746      | 119 (-98%)    |
| erofs wait time (us)  | 357805     | 174205 (-51%) |

| sha256 ramdisk random read | WQ_UNBOUND    | ~WQ_UNBOUND |
|----------------------------|-----------=---|-------------|
| arm64 (accelerated)        | bw=42.4MiB/s  | bw=212MiB/s |
| arm64 (generic)            | bw=16.5MiB/s  | bw=48MiB/s  |
| x86_64 (generic)           | bw=233MiB/s   | bw=230MiB/s |

Cc: Sami Tolvanen <samitolvanen@google.com>
Cc: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Nathan Huckleberry <nhuck@google.com>
---
 drivers/md/dm-verity-target.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
index ccf5b852fbf7..020fd2341025 100644
--- a/drivers/md/dm-verity-target.c
+++ b/drivers/md/dm-verity-target.c
@@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
 		goto bad;
 	}
 
-	/* WQ_UNBOUND greatly improves performance when running on ramdisk */
-	wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
+	wq_flags = WQ_MEM_RECLAIM;
+
 	/*
 	 * Using WQ_HIGHPRI improves throughput and completion latency by
 	 * reducing wait times when reading from a dm-verity device.
-- 
2.39.1.456.gfc5497dd1b-goog
Re: [dm-devel] [PATCH] dm-verity: Remove WQ_UNBOUND.
Posted by Mikulas Patocka 2 years, 7 months ago 

On Wed, 1 Feb 2023, Nathan Huckleberry wrote:

> Setting WQ_UNBOUND increases scheduler latency on ARM64.  This is likely
> due to the asymmetric architecture of ARM64 processors.
> 
> I've been unable to reproduce the results that claim WQ_UNBOUND gives a
> performance boost on x86-64.
> 
> This flag is causing performance issues for multiple subsystems within
> Android.  Notably, the same slowdown exists for decompression with
> EROFS.
> 
> | open-prebuilt-camera  | WQ_UNBOUND | ~WQ_UNBOUND   |
> |-----------------------|------------|---------------|
> | verity wait time (us) | 11746      | 119 (-98%)    |
> | erofs wait time (us)  | 357805     | 174205 (-51%) |
> 
> | sha256 ramdisk random read | WQ_UNBOUND    | ~WQ_UNBOUND |
> |----------------------------|-----------=---|-------------|
> | arm64 (accelerated)        | bw=42.4MiB/s  | bw=212MiB/s |
> | arm64 (generic)            | bw=16.5MiB/s  | bw=48MiB/s  |
> | x86_64 (generic)           | bw=233MiB/s   | bw=230MiB/s |
> 
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> ---
>  drivers/md/dm-verity-target.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index ccf5b852fbf7..020fd2341025 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
>  		goto bad;
>  	}
>  
> -	/* WQ_UNBOUND greatly improves performance when running on ramdisk */
> -	wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
> +	wq_flags = WQ_MEM_RECLAIM;
> +
>  	/*
>  	 * Using WQ_HIGHPRI improves throughput and completion latency by
>  	 * reducing wait times when reading from a dm-verity device.

Hi

If you remove WQ_UNBOUND, you should also change the last argument of 
alloc_workqueue from num_online_cpus() to either 0 or 1. Try both 0 and 1 
and tell us which performs better.

Mikulas
Re: [dm-devel] [PATCH] dm-verity: Remove WQ_UNBOUND.
Posted by Nathan Huckleberry 2 years, 7 months ago 
On Tue, Feb 7, 2023 at 12:16 AM Mikulas Patocka <mpatocka@redhat.com> wrote:
>
>
>
> On Wed, 1 Feb 2023, Nathan Huckleberry wrote:
>
> > Setting WQ_UNBOUND increases scheduler latency on ARM64.  This is likely
> > due to the asymmetric architecture of ARM64 processors.
> >
> > I've been unable to reproduce the results that claim WQ_UNBOUND gives a
> > performance boost on x86-64.
> >
> > This flag is causing performance issues for multiple subsystems within
> > Android.  Notably, the same slowdown exists for decompression with
> > EROFS.
> >
> > | open-prebuilt-camera  | WQ_UNBOUND | ~WQ_UNBOUND   |
> > |-----------------------|------------|---------------|
> > | verity wait time (us) | 11746      | 119 (-98%)    |
> > | erofs wait time (us)  | 357805     | 174205 (-51%) |
> >
> > | sha256 ramdisk random read | WQ_UNBOUND    | ~WQ_UNBOUND |
> > |----------------------------|-----------=---|-------------|
> > | arm64 (accelerated)        | bw=42.4MiB/s  | bw=212MiB/s |
> > | arm64 (generic)            | bw=16.5MiB/s  | bw=48MiB/s  |
> > | x86_64 (generic)           | bw=233MiB/s   | bw=230MiB/s |
> >
> > Cc: Sami Tolvanen <samitolvanen@google.com>
> > Cc: Eric Biggers <ebiggers@kernel.org>
> > Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> > ---
> >  drivers/md/dm-verity-target.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> > index ccf5b852fbf7..020fd2341025 100644
> > --- a/drivers/md/dm-verity-target.c
> > +++ b/drivers/md/dm-verity-target.c
> > @@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> >               goto bad;
> >       }
> >
> > -     /* WQ_UNBOUND greatly improves performance when running on ramdisk */
> > -     wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
> > +     wq_flags = WQ_MEM_RECLAIM;
> > +
> >       /*
> >        * Using WQ_HIGHPRI improves throughput and completion latency by
> >        * reducing wait times when reading from a dm-verity device.
>
> Hi
>
> If you remove WQ_UNBOUND, you should also change the last argument of
> alloc_workqueue from num_online_cpus() to either 0 or 1. Try both 0 and 1
> and tell us which performs better.

They look roughly the same on ARM64. There's a slight advantage for
using 1, but they're too close to conclusively say one is better.

Thanks,
Huck

>
> Mikulas
>
Re: dm-verity: Remove WQ_UNBOUND.
Posted by Mike Snitzer 2 years, 7 months ago 
On Wed, Feb 01 2023 at  8:23P -0500,
Nathan Huckleberry <nhuck@google.com> wrote:

> Setting WQ_UNBOUND increases scheduler latency on ARM64.  This is likely
> due to the asymmetric architecture of ARM64 processors.
> 
> I've been unable to reproduce the results that claim WQ_UNBOUND gives a
> performance boost on x86-64.
> 
> This flag is causing performance issues for multiple subsystems within
> Android.  Notably, the same slowdown exists for decompression with
> EROFS.
> 
> | open-prebuilt-camera  | WQ_UNBOUND | ~WQ_UNBOUND   |
> |-----------------------|------------|---------------|
> | verity wait time (us) | 11746      | 119 (-98%)    |
> | erofs wait time (us)  | 357805     | 174205 (-51%) |
> 
> | sha256 ramdisk random read | WQ_UNBOUND    | ~WQ_UNBOUND |
> |----------------------------|-----------=---|-------------|
> | arm64 (accelerated)        | bw=42.4MiB/s  | bw=212MiB/s |
> | arm64 (generic)            | bw=16.5MiB/s  | bw=48MiB/s  |
> | x86_64 (generic)           | bw=233MiB/s   | bw=230MiB/s |
> 
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Eric Biggers <ebiggers@kernel.org>
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> ---
>  drivers/md/dm-verity-target.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> index ccf5b852fbf7..020fd2341025 100644
> --- a/drivers/md/dm-verity-target.c
> +++ b/drivers/md/dm-verity-target.c
> @@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
>  		goto bad;
>  	}
>  
> -	/* WQ_UNBOUND greatly improves performance when running on ramdisk */
> -	wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
> +	wq_flags = WQ_MEM_RECLAIM;
> +
>  	/*
>  	 * Using WQ_HIGHPRI improves throughput and completion latency by
>  	 * reducing wait times when reading from a dm-verity device.
> -- 
> 2.39.1.456.gfc5497dd1b-goog

Hi,

I've discussed with Mikulas, tweaked your patch slightly but accepted
your change, please see:

https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=6f30cc248507ee96c22ff4c3cbc86099ff12b7a9

Thanks,
Mike
Re: dm-verity: Remove WQ_UNBOUND.
Posted by Nathan Huckleberry 2 years, 7 months ago 
Looks good. Thanks.

On Thu, Feb 2, 2023 at 8:41 AM Mike Snitzer <snitzer@kernel.org> wrote:
>
> On Wed, Feb 01 2023 at  8:23P -0500,
> Nathan Huckleberry <nhuck@google.com> wrote:
>
> > Setting WQ_UNBOUND increases scheduler latency on ARM64.  This is likely
> > due to the asymmetric architecture of ARM64 processors.
> >
> > I've been unable to reproduce the results that claim WQ_UNBOUND gives a
> > performance boost on x86-64.
> >
> > This flag is causing performance issues for multiple subsystems within
> > Android.  Notably, the same slowdown exists for decompression with
> > EROFS.
> >
> > | open-prebuilt-camera  | WQ_UNBOUND | ~WQ_UNBOUND   |
> > |-----------------------|------------|---------------|
> > | verity wait time (us) | 11746      | 119 (-98%)    |
> > | erofs wait time (us)  | 357805     | 174205 (-51%) |
> >
> > | sha256 ramdisk random read | WQ_UNBOUND    | ~WQ_UNBOUND |
> > |----------------------------|-----------=---|-------------|
> > | arm64 (accelerated)        | bw=42.4MiB/s  | bw=212MiB/s |
> > | arm64 (generic)            | bw=16.5MiB/s  | bw=48MiB/s  |
> > | x86_64 (generic)           | bw=233MiB/s   | bw=230MiB/s |
> >
> > Cc: Sami Tolvanen <samitolvanen@google.com>
> > Cc: Eric Biggers <ebiggers@kernel.org>
> > Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> > ---
> >  drivers/md/dm-verity-target.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/md/dm-verity-target.c b/drivers/md/dm-verity-target.c
> > index ccf5b852fbf7..020fd2341025 100644
> > --- a/drivers/md/dm-verity-target.c
> > +++ b/drivers/md/dm-verity-target.c
> > @@ -1399,8 +1399,8 @@ static int verity_ctr(struct dm_target *ti, unsigned argc, char **argv)
> >               goto bad;
> >       }
> >
> > -     /* WQ_UNBOUND greatly improves performance when running on ramdisk */
> > -     wq_flags = WQ_MEM_RECLAIM | WQ_UNBOUND;
> > +     wq_flags = WQ_MEM_RECLAIM;
> > +
> >       /*
> >        * Using WQ_HIGHPRI improves throughput and completion latency by
> >        * reducing wait times when reading from a dm-verity device.
> > --
> > 2.39.1.456.gfc5497dd1b-goog
>
> Hi,
>
> I've discussed with Mikulas, tweaked your patch slightly but accepted
> your change, please see:
>
> https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=6f30cc248507ee96c22ff4c3cbc86099ff12b7a9
>
> Thanks,
> Mike

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