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SubjectRe: [PATCH v2 0/9] Remove spin_unlock_wait()
On Fri, Jul 07, 2017 at 10:31:28AM +0200, Ingo Molnar wrote:
> Here's a quick list of all the use cases:
>
> net/netfilter/nf_conntrack_core.c:
>
> - This is I believe the 'original', historic spin_unlock_wait() usecase that
> still exists in the kernel. spin_unlock_wait() is only used in a rare case,
> when the netfilter hash is resized via nf_conntrack_hash_resize() - which is
> a very heavy operation to begin with. It will no doubt get slower with the
> proposed changes, but it probably does not matter. A networking person
> Acked-by would be nice though.
>
> drivers/ata/libata-eh.c:
>
> - Locking of the ATA port in ata_scsi_cmd_error_handler(), presumably this can
> race with IRQs and ioctls() on other CPUs. Very likely not performance
> sensitive in any fashion, on IO errors things stop for many seconds anyway.
>
> ipc/sem.c:
>
> - A rare race condition branch in the SysV IPC semaphore freeing code in
> exit_sem() - where even the main code flow is not performance sensitive,
> because typical database workloads get their semaphore arrays during startup
> and don't ever do heavy runtime allocation/freeing of them.
>
> kernel/sched/completion.c:
>
> - completion_done(). This is actually a (comparatively) rarely used completion
> API call - almost all the upstream usecases are in drivers, plus two in
> filesystems - neither usecase seems in a performance critical hot path.
> Completions typically involve scheduling and context switching, so in the
> worst case the proposed change adds overhead to a scheduling slow path.
>

You missed the one in do_exit(), which I thought was the original one.

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