On 04/06/2019 07:36 AM, Keith Busch wrote:
> On Fri, Apr 5, 2019 at 5:04 PM Jens Axboe <ax...@kernel.dk> wrote:
>> Looking at current peak testing, I've got around 1.2% in queue enter
>> and exit. It's definitely not free, hence my question. Probably safe
>> to assume that we'll double that cycle counter, per IO.
>
> Okay, that's not negligible at all. I don't know of a faster reference
> than the percpu_ref, but that much overhead would have to rule out
> having a per hctx counter.
>
If there is no faster reference to enable waiting for all inflight requests to
complete, is it possible to re-map (migrate) those requests to other hctx whose
cpus (ctx) are still online, e.g., to extract the bio and re-map those bio to
other ctx (e.g., cpu0)?
One drawback I can see is if 63 out of 64 cpus are suddenly offline, cpu0 would
be stuck.
Dongli Zhang
