Re: [PATCH 00/10] Further reduce overhead of fsnotify permission hooks

[Amir Goldstein <amir73il@gmail.com>]

On Sun, Mar 17, 2024 at 8:42 PM Amir Goldstein <amir73il@gmail.com> wrote:
>
> Jan,
>
> Commit 082fd1ea1f98 ("fsnotify: optimize the case of no parent watcher")
> has reduced the CPU overhead of fsnotify hooks, but we can further
> reduce the overhead of permission event hooks, by avoiding the call to
> fsnotify() and fsnotify_parent() altogether when there are no permission
> event watchers on the sb.
>
> The main motivation for this work was to avoid the overhead that was
> reported by kernel test robot on the patch that adds the upcoming
> per-content event hooks (i.e. FS_PRE_ACCESS/FS_PRE_MODIFY).
>
> Kernel test robot has confirmed that with this series, the addition of
> pre-conent fsnotify hooks does not result in any regression [1].
> Kernet test robot has also reported performance improvements in some
> workloads compared to upstream on an earlier version of this series, but
> still waiting for the final results.

FYI, the results are back [1] and they show clear improvement in two
workloads by this patch set as expected when the permission hooks
are practically being disabled:

---------------- ---------------------------
--------------------------- ---------------------------
         %stddev     %change         %stddev     %change
%stddev     %change         %stddev
             \          |                \          |                \
         |                \
 1.338e+08            +0.4%  1.344e+08            +0.3%  1.342e+08
       +5.8%  1.416e+08        unixbench.throughput
 5.759e+10            +0.4%  5.784e+10            +0.2%  5.772e+10
       +5.8%  6.094e+10        unixbench.workload

Thanks,
Amir.

[1] https://lore.kernel.org/all/Zfj3wxDHolB1qCGO@xsang-OptiPlex-9020/