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Date: Tue, 26 Mar 2024 07:22:29 +0100
From: Christoph Hellwig <hch@lst.de>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Jens Axboe <axboe@kernel.dk>, linux-block@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>, Hannes Reinecke <hare@suse.de>,
	Ming Lei <ming.lei@redhat.com>, Yu Kuai <yukuai3@huawei.com>
Subject: Re: [PATCH v2] block: Improve IOPS by removing the fairness code
Message-ID: <20240326062229.GA7554@lst.de>
References: <20240325221420.1468801-1-bvanassche@acm.org>
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In-Reply-To: <20240325221420.1468801-1-bvanassche@acm.org>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Mon, Mar 25, 2024 at 03:14:19PM -0700, Bart Van Assche wrote:
> On my test setup (x86 VM with 72 CPU cores) this patch results in 2.9% more
> IOPS. IOPS have been measured as follows:
> 
> $ modprobe null_blk nr_devices=1 completion_nsec=0
> $ fio --bs=4096 --disable_clat=1 --disable_slat=1 --group_reporting=1 \
>       --gtod_reduce=1 --invalidate=1 --ioengine=psync --ioscheduler=none \
>       --norandommap --runtime=60 --rw=randread --thread --time_based=1 \
>       --buffered=0 --numjobs=64 --name=/dev/nullb0 --filename=/dev/nullb0

And how does it behave when you have multiple request_queues sharing
a tag_set with very unevent use that could cause one to starve all
the tags?  Because that is what this code exists for.