linux-kernel - Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for read

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Message-ID: <20200917144648.GA31086@infradead.org>
Date:   Thu, 17 Sep 2020 15:46:48 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Boaz Harrosh <boaz@...xistor.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>, Hou Tao <houtao1@...wei.com>,
        peterz@...radead.org, Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Jan Kara <jack@...e.cz>
Subject: Re: [RFC PATCH] locking/percpu-rwsem: use this_cpu_{inc|dec}() for
 read_count

On Thu, Sep 17, 2020 at 04:46:38PM +0300, Boaz Harrosh wrote:
> From my totally subjective experience on the filesystem side (user of
> bio_endio) all HW block drivers I used including Nvme isci, sata... etc. end
> up calling bio_endio in softirq. The big exception to that is the vdX
> drivers under KVM. Which is very Ironic to me.

NVMe normally calls it from hardirq or IPI context.  The only time it
would use softirq context is if you have a single I/O queue, which is
very unusual.