linux-ext4 - Re: [PATCH] block: enable per-cpu bio cache by default

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Message-ID: <CALWNXx_J5L1fjTrVA5ChXsPdGk5E5HSuNHUO183mVat6GZdo=g@mail.gmail.com>
Date: Mon, 13 Oct 2025 13:44:19 +0800
From: fengnan chang <fengnanchang@...il.com>
To: Ming Lei <ming.lei@...hat.com>
Cc: Fengnan Chang <changfengnan@...edance.com>, axboe@...nel.dk, viro@...iv.linux.org.uk, 
	brauner@...nel.org, jack@...e.cz, asml.silence@...il.com, willy@...radead.org, 
	djwong@...nel.org, hch@...radead.org, ritesh.list@...il.com, 
	linux-fsdevel@...r.kernel.org, io-uring@...r.kernel.org, 
	linux-xfs@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] block: enable per-cpu bio cache by default

On Mon, Oct 13, 2025 at 1:19 PM Ming Lei <ming.lei@...hat.com> wrote:
>
> On Sat, Oct 11, 2025 at 09:33:12AM +0800, Fengnan Chang wrote:
> > Per cpu bio cache was only used in the io_uring + raw block device,
> > after commit 12e4e8c7ab59 ("io_uring/rw: enable bio caches for IRQ
> > rw"),  bio_put is safe for task and irq context, bio_alloc_bioset is
> > safe for task context and no one calls in irq context, so we can enable
> > per cpu bio cache by default.
> >
> > Benchmarked with t/io_uring and ext4+nvme:
> > taskset -c 6 /root/fio/t/io_uring  -p0 -d128 -b4096 -s1 -c1 -F1 -B1 -R1
> > -X1 -n1 -P1  /mnt/testfile
> > base IOPS is 562K, patch IOPS is 574K. The CPU usage of bio_alloc_bioset
> > decrease from 1.42% to 1.22%.
> >
> > The worst case is allocate bio in CPU A but free in CPU B, still use
> > t/io_uring and ext4+nvme:
> > base IOPS is 648K, patch IOPS is 647K.
>
> Just be curious, how do you run the remote bio free test? If the nvme is 1:1
> mapping, you may not trigger it.

I modified the nvme driver, reduce the number of queues.

>
> BTW, ublk has this kind of remote bio free trouble, but not see IOPS drop
> with this patch.
>
> The patch itself looks fine for me.
>
>
> Thanks,
> Ming
>
>