Re: [PATCH v2 2/2] nvme-multipath: don't wait for a grace period in nvme_mpath_set_live()

[Nilay Shroff <nilay@linux.ibm.com>]

On 11/11/26 6:40 PM, Qiliang Yuan wrote:
> When a path goes live, nvme_mpath_set_live() waits for an SRCU grace
> period of the namespace head before kicking the requeue work, so that
> bios which found no usable path are on the requeue list by the time it
> runs.
> 
> The ANA work calls nvme_mpath_set_live() for every namespace that
> becomes optimized or non-optimized, one after another, so an ANA change
> waits for one grace period per namespace.
> 
> Start the grace period with start_poll_synchronize_srcu() instead and
> have nvme_requeue_work() wait for it only if it has not completed yet.
> Take the cookie under head->lock, so that concurrent callers store
> their cookies in order and the requeue work never sees an older one.
> The grace periods of all namespaces then run in parallel, and requeue
> work kicked for other reasons finds the cookie completed and does not
> wait.
> 
> Flipping an ANA group from inaccessible to optimized ten times over
> nvme-tcp loopback, nvme_read_ana_log() takes (median, min-max in
> parentheses):
> 
>    namespaces  before (ms)          after (ms)        change
>           256  51.9 (42.5-85.4)     8.9 (2.6-12.0)      -83%
>          1024  157.5 (133.5-179.6)  49.5 (32.8-67.1)    -69%
> 
> Signed-off-by: Qiliang Yuan<qiliang.yuan@linux.dev>

Looks good to me:

Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>