alloc_fd() has a sanity check inside to make sure the struct file mapping to the
allocated fd is NULL. Remove this sanity check since it can be assured by
exisitng zero initilization and NULL set when recycling fd. Meanwhile, add
likely/unlikely and expand_file() call avoidance to reduce the work under
file_lock.
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Yu Ma <yu.ma@intel.com>
---
fs/file.c | 33 ++++++++++++++-------------------
1 file changed, 14 insertions(+), 19 deletions(-)
diff --git a/fs/file.c b/fs/file.c
index a3b72aa64f11..e1b9d6df7941 100644
--- a/fs/file.c
+++ b/fs/file.c
@@ -515,7 +515,7 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags)
if (fd < files->next_fd)
fd = files->next_fd;
- if (fd < fdt->max_fds)
+ if (likely(fd < fdt->max_fds))
fd = find_next_fd(fdt, fd);
/*
@@ -523,19 +523,21 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags)
* will limit the total number of files that can be opened.
*/
error = -EMFILE;
- if (fd >= end)
+ if (unlikely(fd >= end))
goto out;
- error = expand_files(files, fd);
- if (error < 0)
- goto out;
+ if (unlikely(fd >= fdt->max_fds)) {
+ error = expand_files(files, fd);
+ if (error < 0)
+ goto out;
- /*
- * If we needed to expand the fs array we
- * might have blocked - try again.
- */
- if (error)
- goto repeat;
+ /*
+ * If we needed to expand the fs array we
+ * might have blocked - try again.
+ */
+ if (error)
+ goto repeat;
+ }
if (start <= files->next_fd)
files->next_fd = fd + 1;
@@ -546,13 +548,6 @@ static int alloc_fd(unsigned start, unsigned end, unsigned flags)
else
__clear_close_on_exec(fd, fdt);
error = fd;
-#if 1
- /* Sanity check */
- if (rcu_access_pointer(fdt->fd[fd]) != NULL) {
- printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
- rcu_assign_pointer(fdt->fd[fd], NULL);
- }
-#endif
out:
spin_unlock(&files->file_lock);
@@ -618,7 +613,7 @@ void fd_install(unsigned int fd, struct file *file)
rcu_read_unlock_sched();
spin_lock(&files->file_lock);
fdt = files_fdtable(files);
- BUG_ON(fdt->fd[fd] != NULL);
+ WARN_ON(fdt->fd[fd] != NULL);
rcu_assign_pointer(fdt->fd[fd], file);
spin_unlock(&files->file_lock);
return;
--
2.43.0On Wed, Jul 17, 2024 at 10:50:16AM -0400, Yu Ma wrote:
> alloc_fd() has a sanity check inside to make sure the struct file mapping to the
> allocated fd is NULL. Remove this sanity check since it can be assured by
> exisitng zero initilization and NULL set when recycling fd. Meanwhile, add
> likely/unlikely and expand_file() call avoidance to reduce the work under
> file_lock.
> + if (unlikely(fd >= fdt->max_fds)) {
> + error = expand_files(files, fd);
> + if (error < 0)
> + goto out;
>
> - /*
> - * If we needed to expand the fs array we
> - * might have blocked - try again.
> - */
> - if (error)
> - goto repeat;
> + /*
> + * If we needed to expand the fs array we
> + * might have blocked - try again.
> + */
> + if (error)
> + goto repeat;
With that change you can't get 0 from expand_files() here, so the
last goto should be unconditional. The only case when expand_files()
returns 0 is when it has found the descriptor already being covered
by fdt; since fdt->max_fds is stabilized by ->files_lock we are
holding here, comparison in expand_files() will give the same
result as it just had.
IOW, that goto repeat should be unconditional. The fun part here is
that this was the only caller that distinguished between 0 and 1...
On 8/15/2024 5:38 AM, Al Viro wrote:
> On Wed, Jul 17, 2024 at 10:50:16AM -0400, Yu Ma wrote:
>> alloc_fd() has a sanity check inside to make sure the struct file mapping to the
>> allocated fd is NULL. Remove this sanity check since it can be assured by
>> exisitng zero initilization and NULL set when recycling fd. Meanwhile, add
>> likely/unlikely and expand_file() call avoidance to reduce the work under
>> file_lock.
>> + if (unlikely(fd >= fdt->max_fds)) {
>> + error = expand_files(files, fd);
>> + if (error < 0)
>> + goto out;
>>
>> - /*
>> - * If we needed to expand the fs array we
>> - * might have blocked - try again.
>> - */
>> - if (error)
>> - goto repeat;
>> + /*
>> + * If we needed to expand the fs array we
>> + * might have blocked - try again.
>> + */
>> + if (error)
>> + goto repeat;
> With that change you can't get 0 from expand_files() here, so the
> last goto should be unconditional. The only case when expand_files()
> returns 0 is when it has found the descriptor already being covered
> by fdt; since fdt->max_fds is stabilized by ->files_lock we are
> holding here, comparison in expand_files() will give the same
> result as it just had.
>
> IOW, that goto repeat should be unconditional. The fun part here is
> that this was the only caller that distinguished between 0 and 1...
Yes, thanks Al, fully agree with you. The if (error) could be removed
here as the above unlikely would make sure no 0 return here. Should I
submit another version of patch set to update it, or you may help to
update it directly during merge? I'm not very familiar with the rules,
please let me know if I'd update and I'll take action soon. Thanks again
for your careful check here.
On Thu, Aug 15, 2024 at 10:49:40AM +0800, Ma, Yu wrote: > Yes, thanks Al, fully agree with you. The if (error) could be removed here > as the above unlikely would make sure no 0 return here. Should I submit > another version of patch set to update it, or you may help to update it > directly during merge? I'm not very familiar with the rules, please let me > know if I'd update and I'll take action soon. Thanks again for your careful > check here. See the current work.fdtable...
On Thu, Aug 15, 2024 at 5:45 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > On Thu, Aug 15, 2024 at 10:49:40AM +0800, Ma, Yu wrote: > > > Yes, thanks Al, fully agree with you. The if (error) could be removed here > > as the above unlikely would make sure no 0 return here. Should I submit > > another version of patch set to update it, or you may help to update it > > directly during merge? I'm not very familiar with the rules, please let me > > know if I'd update and I'll take action soon. Thanks again for your careful > > check here. > > See the current work.fdtable... this patchset seems to have fallen through the cracks. anything holding up the merge? -- Mateusz Guzik <mjguzik gmail.com>
On Thu, Oct 31, 2024 at 08:42:18AM +0100, Mateusz Guzik wrote: > On Thu, Aug 15, 2024 at 5:45 AM Al Viro <viro@zeniv.linux.org.uk> wrote: > > > > On Thu, Aug 15, 2024 at 10:49:40AM +0800, Ma, Yu wrote: > > > > > Yes, thanks Al, fully agree with you. The if (error) could be removed here > > > as the above unlikely would make sure no 0 return here. Should I submit > > > another version of patch set to update it, or you may help to update it > > > directly during merge? I'm not very familiar with the rules, please let me > > > know if I'd update and I'll take action soon. Thanks again for your careful > > > check here. > > > > See the current work.fdtable... > > this patchset seems to have fallen through the cracks. anything > holding up the merge? It's in next for this merge window.
On 8/15/2024 11:45 AM, Al Viro wrote: > On Thu, Aug 15, 2024 at 10:49:40AM +0800, Ma, Yu wrote: > >> Yes, thanks Al, fully agree with you. The if (error) could be removed here >> as the above unlikely would make sure no 0 return here. Should I submit >> another version of patch set to update it, or you may help to update it >> directly during merge? I'm not very familiar with the rules, please let me >> know if I'd update and I'll take action soon. Thanks again for your careful >> check here. > See the current work.fdtable... Saw it, thanks :)
Hello,
kernel test robot noticed a 1.2% improvement of will-it-scale.per_process_ops on:
commit: f1139c8e66d5c618aad04a93a2378ad9586464f9 ("[PATCH v5 1/3] fs/file.c: remove sanity_check and add likely/unlikely in alloc_fd()")
url: https://github.com/intel-lab-lkp/linux/commits/Yu-Ma/fs-file-c-remove-sanity_check-and-add-likely-unlikely-in-alloc_fd/20240717-224830
base: https://git.kernel.org/cgit/linux/kernel/git/vfs/vfs.git vfs.all
patch link: https://lore.kernel.org/all/20240717145018.3972922-2-yu.ma@intel.com/
patch subject: [PATCH v5 1/3] fs/file.c: remove sanity_check and add likely/unlikely in alloc_fd()
testcase: will-it-scale
test machine: 256 threads 2 sockets GENUINE INTEL(R) XEON(R) (Sierra Forest) with 128G memory
parameters:
nr_task: 100%
mode: process
test: dup1
cpufreq_governor: performance
Details are as below:
-------------------------------------------------------------------------------------------------->
The kernel config and materials to reproduce are available at:
https://download.01.org/0day-ci/archive/20240806/202408062146.832faa23-oliver.sang@intel.com
=========================================================================================
compiler/cpufreq_governor/kconfig/mode/nr_task/rootfs/tbox_group/test/testcase:
gcc-13/performance/x86_64-rhel-8.3/process/100%/debian-12-x86_64-20240206.cgz/lkp-srf-2sp1/dup1/will-it-scale
commit:
5f30e082ab ("Merge branch 'vfs.iomap' into vfs.all")
f1139c8e66 ("fs/file.c: remove sanity_check and add likely/unlikely in alloc_fd()")
5f30e082ab8b3431 f1139c8e66d5c618aad04a93a23
---------------- ---------------------------
%stddev %change %stddev
\ | \
377983 ± 69% +74.1% 658036 ± 17% numa-meminfo.node0.AnonPages
18.17 ± 10% -48.6% 9.33 ± 35% perf-c2c.DRAM.local
8.796e+08 +1.2% 8.903e+08 will-it-scale.256.processes
3436082 +1.2% 3477810 will-it-scale.per_process_ops
8.796e+08 +1.2% 8.903e+08 will-it-scale.workload
1.517e+11 -4.3% 1.452e+11 perf-stat.i.branch-instructions
0.03 ± 8% +0.0 0.04 ± 36% perf-stat.i.branch-miss-rate%
0.93 +3.9% 0.96 perf-stat.i.cpi
7.13e+11 -3.5% 6.88e+11 perf-stat.i.instructions
1.08 -3.4% 1.04 perf-stat.i.ipc
0.93 +3.4% 0.96 perf-stat.overall.cpi
1.08 -3.3% 1.04 perf-stat.overall.ipc
245130 -4.4% 234451 perf-stat.overall.path-length
1.512e+11 -4.3% 1.447e+11 perf-stat.ps.branch-instructions
7.106e+11 -3.5% 6.857e+11 perf-stat.ps.instructions
2.156e+14 -3.2% 2.087e+14 perf-stat.total.instructions
14.90 -0.7 14.20 perf-profile.calltrace.cycles-pp.do_syscall_64.entry_SYSCALL_64_after_hwframe.dup
12.01 -0.7 11.32 perf-profile.calltrace.cycles-pp.__x64_sys_dup.do_syscall_64.entry_SYSCALL_64_after_hwframe.dup
16.54 -0.7 15.88 perf-profile.calltrace.cycles-pp.entry_SYSCALL_64_after_hwframe.dup
6.44 -0.6 5.89 perf-profile.calltrace.cycles-pp.alloc_fd.__x64_sys_dup.do_syscall_64.entry_SYSCALL_64_after_hwframe.dup
2.86 -0.0 2.82 perf-profile.calltrace.cycles-pp.entry_SYSRETQ_unsafe_stack.__close
8.94 -0.0 8.90 perf-profile.calltrace.cycles-pp.filp_flush.__x64_sys_close.do_syscall_64.entry_SYSCALL_64_after_hwframe.__close
7.76 -0.0 7.72 perf-profile.calltrace.cycles-pp.locks_remove_posix.filp_flush.__x64_sys_close.do_syscall_64.entry_SYSCALL_64_after_hwframe
2.58 -0.0 2.54 perf-profile.calltrace.cycles-pp.__fput_sync.__x64_sys_close.do_syscall_64.entry_SYSCALL_64_after_hwframe.__close
1.11 -0.0 1.10 perf-profile.calltrace.cycles-pp.syscall_exit_to_user_mode.do_syscall_64.entry_SYSCALL_64_after_hwframe.__close
1.33 +0.0 1.35 perf-profile.calltrace.cycles-pp.testcase
0.54 +0.0 0.56 perf-profile.calltrace.cycles-pp.x64_sys_call.do_syscall_64.entry_SYSCALL_64_after_hwframe.__close
0.79 +0.0 0.82 perf-profile.calltrace.cycles-pp.entry_SYSCALL_64_safe_stack.dup
1.33 +0.0 1.37 perf-profile.calltrace.cycles-pp.close@plt
2.73 +0.1 2.78 perf-profile.calltrace.cycles-pp._raw_spin_lock.file_close_fd.__x64_sys_close.do_syscall_64.entry_SYSCALL_64_after_hwframe
1.05 +0.1 1.11 perf-profile.calltrace.cycles-pp.syscall_exit_to_user_mode.do_syscall_64.entry_SYSCALL_64_after_hwframe.dup
4.35 +0.1 4.42 perf-profile.calltrace.cycles-pp.file_close_fd.__x64_sys_close.do_syscall_64.entry_SYSCALL_64_after_hwframe.__close
22.18 +0.3 22.51 perf-profile.calltrace.cycles-pp.entry_SYSCALL_64.__close
21.50 ± 2% +1.5 23.02 perf-profile.calltrace.cycles-pp.entry_SYSCALL_64.dup
12.10 -0.7 11.39 perf-profile.children.cycles-pp.__x64_sys_dup
34.79 -0.7 34.12 perf-profile.children.cycles-pp.do_syscall_64
38.04 -0.6 37.42 perf-profile.children.cycles-pp.entry_SYSCALL_64_after_hwframe
6.48 -0.6 5.90 perf-profile.children.cycles-pp.alloc_fd
1.86 -0.5 1.41 perf-profile.children.cycles-pp.syscall_return_via_sysret
0.57 -0.1 0.47 perf-profile.children.cycles-pp.fd_install
9.11 -0.0 9.07 perf-profile.children.cycles-pp.filp_flush
7.93 -0.0 7.89 perf-profile.children.cycles-pp.locks_remove_posix
2.61 -0.0 2.58 perf-profile.children.cycles-pp.__fput_sync
1.16 +0.0 1.18 perf-profile.children.cycles-pp.x64_sys_call
0.05 +0.0 0.07 ± 13% perf-profile.children.cycles-pp.clockevents_program_event
0.51 +0.0 0.53 perf-profile.children.cycles-pp.syscall_exit_to_user_mode_prepare
2.17 +0.0 2.20 perf-profile.children.cycles-pp.syscall_exit_to_user_mode
5.72 +0.0 5.75 perf-profile.children.cycles-pp._raw_spin_lock
2.10 +0.0 2.13 perf-profile.children.cycles-pp.testcase
2.02 +0.0 2.06 perf-profile.children.cycles-pp.entry_SYSCALL_64_safe_stack
0.13 ± 2% +0.0 0.17 perf-profile.children.cycles-pp.dup@plt
4.38 +0.1 4.46 perf-profile.children.cycles-pp.file_close_fd
23.00 +0.1 23.11 perf-profile.children.cycles-pp.entry_SYSRETQ_unsafe_stack
59.27 +0.5 59.73 perf-profile.children.cycles-pp.__close
28.73 +1.1 29.80 perf-profile.children.cycles-pp.entry_SYSCALL_64
1.86 -0.5 1.41 perf-profile.self.cycles-pp.syscall_return_via_sysret
2.28 -0.2 2.12 perf-profile.self.cycles-pp.alloc_fd
0.54 -0.1 0.43 perf-profile.self.cycles-pp.fd_install
7.87 -0.0 7.83 perf-profile.self.cycles-pp.locks_remove_posix
2.47 -0.0 2.44 perf-profile.self.cycles-pp.__fput_sync
1.23 +0.0 1.24 perf-profile.self.cycles-pp.file_close_fd_locked
1.09 +0.0 1.11 perf-profile.self.cycles-pp.x64_sys_call
0.51 +0.0 0.53 perf-profile.self.cycles-pp.syscall_exit_to_user_mode_prepare
1.29 +0.0 1.32 perf-profile.self.cycles-pp.testcase
5.66 +0.0 5.69 perf-profile.self.cycles-pp._raw_spin_lock
1.95 +0.0 1.99 perf-profile.self.cycles-pp.entry_SYSCALL_64_safe_stack
2.85 +0.0 2.90 perf-profile.self.cycles-pp.entry_SYSCALL_64_after_hwframe
0.02 ±141% +0.0 0.06 ± 13% perf-profile.self.cycles-pp.ktime_get
0.00 +0.1 0.07 perf-profile.self.cycles-pp.dup@plt
22.93 +0.1 23.05 perf-profile.self.cycles-pp.entry_SYSRETQ_unsafe_stack
10.11 +0.2 10.34 perf-profile.self.cycles-pp.dup
13.70 +0.3 13.98 perf-profile.self.cycles-pp.entry_SYSCALL_64
9.84 ± 3% +0.7 10.51 perf-profile.self.cycles-pp.__close
Disclaimer:
Results have been estimated based on internal Intel analysis and are provided
for informational purposes only. Any difference in system hardware or software
design or configuration may affect actual performance.
--
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki
© 2016 - 2025 Red Hat, Inc.