Re: [linus:master] [xfs] 9b64ca202f: fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec 24.1% regression

From: Oliver Sang

Date: Sun Jul 19 2026 - 04:16:49 EST

hi, Christoph Hellwig,

On Fri, Jul 17, 2026 at 08:48:07AM +0200, Christoph Hellwig wrote:
> On Thu, Jul 16, 2026 at 09:13:19PM +0800, kernel test robot wrote:
> >
> >
> > Hello,
> >
> > kernel test robot noticed a 24.1% regression of fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec on:
> >
>
> This looks really odd. While the patch adds a bit more computation,
> that is very cheap shifting and masking.

in order to avoid the false positive, we rebuilt the kernel and rerun tests
on both 9b64ca202f and its parent. though the data has some differences with
last time, the regression trend is still similar - 21.8% regression this time.

> So the only theory I have here
> is that this somehow affects the inode data layout. Can you re-run this
> with the patch below applied on top of commit
> 9b64ca202f364a6bf8e19bdd20953bc2d776c67f ?

yeah, but applying your patch upon 9b64ca202f, we saw the regression recovered.

from average data, it now becomes even little better than the parent of
9b64ca202f, i.e. caffb4252c, but since the data is not very stable - 4% stddev
for caffb4252c and 6% stddev for bd79e961ea, we cannot call +3.1% a valid
improvement according to our bot's rules.

=========================================================================================
compiler/cpufreq_governor/directio/disk/fstype/kconfig/media/rootfs/tbox_group/test/testcase/thread_nr:
gcc-14/performance/bufferedio/1SSD/xfs/x86_64-rhel-9.4/ssd/debian-13-x86_64-20250902.cgz/lkp-icl-2sp8/DRBH/fxmark/4

commit:
caffb4252c ("xfs: massage xfs_imap_to_bp into xfs_read_icluster")
9b64ca202f ("xfs: store an agbno in struct xfs_imap")
bd79e961ea <--- your patch applied upon 9b64ca202f

caffb4252cf15c5c 9b64ca202f364a6bf8e19bdd209 bd79e961eab5806b5c1321fba4d
---------------- --------------------------- ---------------------------
%stddev %change %stddev %change %stddev
\ | \ | \
3.421e+08 ± 4% -21.8% 2.674e+08 ± 3% +3.1% 3.527e+08 ± 6% fxmark.ssd_xfs_DRBH_4_bufferedio.works
6842338 ± 4% -21.8% 5348962 ± 3% +3.1% 7054630 ± 6% fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec
21677 +2.3% 22181 +2.3% 22177 proc-vmstat.nr_mapped
2.54 ± 6% -15.1% 2.15 ± 7% +2.5% 2.60 ± 7% time.user_time
87.25 ± 61% +74.6% 152.38 ± 10% +29.9% 113.38 ± 17% perf-sched.wait_and_delay.count.perf_trace_sched_switch.preempt_schedule_thunk.filemap_get_read_batch.filemap_get_pages.filemap_read
2.18 ± 48% +45.8% 3.18 ± 11% +46.7% 3.20 ± 10% perf-sched.wait_time.avg.ms.perf_trace_sched_switch.exit_to_user_mode_loop.do_syscall_64.entry_SYSCALL_64_after_hwframe.[unknown]
6.89 ±123% -2.7 4.16 ±122% -2.1 4.82 ±131% perf-profile.calltrace.cycles-pp.cpu_startup_entry.start_secondary.common_startup_64
6.89 ±123% -2.7 4.16 ±122% -2.1 4.82 ±131% perf-profile.calltrace.cycles-pp.do_idle.cpu_startup_entry.start_secondary.common_startup_64
6.89 ±123% -2.7 4.16 ±122% -2.1 4.82 ±131% perf-profile.calltrace.cycles-pp.start_secondary.common_startup_64
6.46 ±119% -2.3 4.16 ±122% -1.6 4.82 ±131% perf-profile.calltrace.cycles-pp.cpuidle_enter.cpuidle_idle_call.do_idle.cpu_startup_entry.start_secondary
6.46 ±119% -2.3 4.16 ±122% -1.6 4.82 ±131% perf-profile.calltrace.cycles-pp.cpuidle_idle_call.do_idle.cpu_startup_entry.start_secondary.common_startup_64
3.86 ± 78% -2.2 1.61 ±182% -2.4 1.44 ±179% perf-profile.calltrace.cycles-pp.tear_down_vmas.exit_mmap.__mmput.exit_mm.do_exit
5.44 ±102% -1.5 3.94 ± 80% -3.4 2.03 ±130% perf-profile.calltrace.cycles-pp.free_pgtables.exit_mmap.__mmput.exit_mm.do_exit
4.84 ± 94% -3.0 1.82 ±175% -2.1 2.72 ±103% perf-profile.children.cycles-pp.mutex_unlock
6.89 ±123% -2.7 4.16 ±122% -2.1 4.82 ±131% perf-profile.children.cycles-pp.start_secondary
3.86 ± 78% -2.2 1.61 ±182% -2.4 1.44 ±179% perf-profile.children.cycles-pp.tear_down_vmas
5.44 ±102% -1.5 3.94 ± 80% -3.4 2.03 ±130% perf-profile.children.cycles-pp.free_pgtables
4.87 ± 82% +11.6 16.52 ±191% -1.3 3.57 ±173% perf-profile.children.cycles-pp.__free_one_page
4.84 ± 94% -3.0 1.82 ±175% -2.1 2.72 ±103% perf-profile.self.cycles-pp.mutex_unlock
4.87 ± 82% +10.8 15.63 ±205% -1.3 3.57 ±173% perf-profile.self.cycles-pp.__free_one_page

also list detail data this time FYI, we run tests upon each commit 8 times.

caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json: "fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec": [
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 6178184.745545,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 7016379.89853,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 7178664.672853,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 6975768.767642,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 6671251.242517,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 7013871.524931,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 6760219.644392,
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- 6944366.470556
caffb4252cf15c5c3bbe7ff1f48f24f4015edb9c/matrix.json- ],

9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json: "fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec": [
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5435146.379538,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5468530.366732,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5618409.657153,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5184486.744613,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5118827.985859,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5623235.76661,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5250286.871274,
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- 5092777.109583
9b64ca202f364a6bf8e19bdd20953bc2d776c67f/matrix.json- ],

bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json: "fxmark.ssd_xfs_DRBH_4_bufferedio.works/sec": [
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 7501136.809977,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 7459447.66,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 6360107.595015,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 6922348.764845,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 7658169.213152,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 6741170.118107,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 7321403.278841,
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- 6473261.205802
bd79e961eab5806b5c1321fba4d0dcd6f2168711/matrix.json- ],

>
> diff --git a/fs/xfs/libxfs/xfs_inode_buf.h b/fs/xfs/libxfs/xfs_inode_buf.h
> index 57192adc7744..319e83d4a087 100644
> --- a/fs/xfs/libxfs/xfs_inode_buf.h
> +++ b/fs/xfs/libxfs/xfs_inode_buf.h
> @@ -15,6 +15,7 @@ struct xfs_dinode;
> */
> struct xfs_imap {
> xfs_agblock_t im_agbno; /* starting agbno of inode cluster */
> + uint32_t __im_pad;
> unsigned short im_boffset; /* offset in inode cluster in bytes */
> };
>