Re: [PATCH v7 4/4] vfs: Use per-cpu list for superblock's inode list

[Jan Kara]

On Tue 12-04-16 18:54:46, Waiman Long wrote:
> When many threads are trying to add or delete inode to or from
> a superblock's s_inodes list, spinlock contention on the list can
> become a performance bottleneck.
> 
> This patch changes the s_inodes field to become a per-cpu list with
> per-cpu spinlocks. As a result, the following superblock inode list
> (sb->s_inodes) iteration functions in vfs are also being modified:
> 
>  1. iterate_bdevs()
>  2. drop_pagecache_sb()
>  3. wait_sb_inodes()
>  4. evict_inodes()
>  5. invalidate_inodes()
>  6. fsnotify_unmount_inodes()
>  7. add_dquot_ref()
>  8. remove_dquot_ref()
> 
> With an exit microbenchmark that creates a large number of threads,
> attachs many inodes to them and then exits. The runtimes of that
> microbenchmark with 1000 threads before and after the patch on a
> 4-socket Intel E7-4820 v3 system (40 cores, 80 threads) were as
> follows:
> 
>   Kernel            Elapsed Time    System Time
>   ------            ------------    -----------
>   Vanilla 4.5-rc4      65.29s         82m14s
>   Patched 4.5-rc4      22.81s         23m03s
> 
> Before the patch, spinlock contention at the inode_sb_list_add()
> function at the startup phase and the inode_sb_list_del() function at
> the exit phase were about 79% and 93% of total CPU time respectively
> (as measured by perf). After the patch, the percpu_list_add()
> function consumed only about 0.04% of CPU time at startup phase. The
> percpu_list_del() function consumed about 0.4% of CPU time at exit
> phase. There were still some spinlock contention, but they happened
> elsewhere.
> 
> Signed-off-by: Waiman Long <Waiman.Long@xxxxxxx>

The patch looks good to me. You can add:

Reviewed-by: Jan Kara <jack@xxxxxxx>

								Honza
-- 
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR