* Waiman Long <waiman.l...@hpe.com> wrote:
> The inode_sb_list_add() and inode_sb_list_del() functions in the vfs
> layer just perform list addition and deletion under lock. So they can
> use the new list batching facility to speed up the list operations
> when many CPUs are trying to do it simultaneously.
>
> In particular, the inode_sb_list_del() function can be a performance
> bottleneck when large applications with many threads and associated
> inodes exit. 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 (48 cores, 96 threads) were
> as follows:
>
> Kernel Elapsed Time System Time
> ------ ------------ -----------
> Vanilla 4.4 65.29s 82m14s
> Patched 4.4 45.69s 49m44s
>
> The elapsed time and the reported system time were reduced by 30%
> and 40% respectively.
That's pretty impressive!
I'm wondering, why are inode_sb_list_add()/del() even called for a presumably
reasonably well cached benchmark running on a system with enough RAM? Are these
perhaps thousands of temporary files, already deleted, and released when all
the
file descriptors are closed as part of sys_exit()?
If that's the case then I suspect an even bigger win would be not just to batch
the (sb-)global list fiddling, but to potentially turn the sb list into a
percpu_alloc() managed set of per CPU lists? It's a bigger change, but it could
speed up a lot of other temporary file intensive usecases as well, not just
batched delete.
Thanks,
Ingo
