Messages in this thread Patch in this message | | | From | Gulam Mohamed <> | Subject | RE: [PATCH V2] Consider inflight IO in io accounting for high latency devices | Date | Mon, 16 Oct 2023 20:01:22 +0000 |
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Hi Bart,
Thanks for your review. Can you please see my inline comments?
Regards, Gulam Mohamed.
-----Original Message----- From: Bart Van Assche <bvanassche@acm.org> Sent: Saturday, October 14, 2023 2:43 AM To: Gulam Mohamed <gulam.mohamed@oracle.com>; axboe@kernel.dk; linux-block@vger.kernel.org; linux-kernel@vger.kernel.org Subject: Re: [PATCH V2] Consider inflight IO in io accounting for high latency devices
On 10/13/23 12:55, Gulam Mohamed wrote: > @@ -1015,7 +1018,13 @@ static inline void blk_account_io_start(struct request *req) > req->part = req->q->disk->part0; > > part_stat_lock(); > - update_io_ticks(req->part, jiffies, false); > + > + if (req->q->nr_hw_queues == 1) { > + hctx = xa_load(&req->q->hctx_table, 0); > + inflight = blk_mq_hctx_has_tags(hctx); > + } > + > + update_io_ticks(req->part, jiffies, inflight); > part_stat_unlock(); > } > }
blk_account_io_start() is called by blk_mq_bio_to_request(). So if I/O statistics are enabled and if there is only a single hardware queue, blk_mq_hctx_has_tags() will be called every time a bio is submitted? The blk_mq_hctx_has_tags() function iterates over all tags. I would be surprised if anyone would consider the overhead of this approach acceptable.
[GULAM]: Yes, it will be called for every submitted bio but for the high latency devices it will not have much impact. This is indicated by the latency figures I provided in the review mail, with and without our patch.
Thanks,
Bart.
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