On Sun, Mar 17, 2024 at 8:42 PM Amir Goldstein <amir73il@xxxxxxxxx> 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/
