From: Christoph Hellwig <hch@infradead.org>
To: Keith Busch <keith.busch@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>,
linux-nvme@lists.infradead.org, Ming Lei <ming.lei@redhat.com>,
Keith Busch <keith.busch@intel.com>,
Jianchao Wang <jianchao.w.wang@oracle.com>,
Keith Busch <kbusch@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH] blk-mq: Wait for for hctx requests on CPU unplug
Date: Sun, 7 Apr 2019 00:51:23 -0700 [thread overview]
Message-ID: <20190407075123.GA22003@infradead.org> (raw)
In-Reply-To: <CAOSXXT7V3E2j_Ut=hJ2X3QcdLwuWGRFtgzTs4iTe+RDMeHg8nA@mail.gmail.com>
On Fri, Apr 05, 2019 at 05:36:32PM -0600, Keith Busch wrote:
> On Fri, Apr 5, 2019 at 5:04 PM Jens Axboe <axboe@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.
Can we just replace queue_enter/exit with the per-hctx reference
entirely?
next prev parent reply other threads:[~2019-04-07 7:51 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-05 21:59 [PATCH] blk-mq: Wait for for hctx requests on CPU unplug Keith Busch
2019-04-05 22:23 ` Jens Axboe
2019-04-05 22:37 ` Keith Busch
2019-04-05 23:04 ` Jens Axboe
2019-04-05 23:36 ` Keith Busch
2019-04-06 9:44 ` Dongli Zhang
2019-04-06 21:27 ` Ming Lei
2019-04-07 13:55 ` Dongli Zhang
2019-04-08 9:49 ` Ming Lei
2019-04-08 15:36 ` Keith Busch
2019-04-08 15:21 ` Keith Busch
2019-04-07 7:51 ` Christoph Hellwig [this message]
2019-04-08 15:23 ` Keith Busch
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