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Date:   Fri, 20 May 2022 17:39:40 +0200
From:   "Jason A. Donenfeld" <Jason@zx2c4.com>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Theodore Ts'o <tytso@mit.edu>, Christoph Hellwig <hch@lst.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro
Message-ID: <Yoe2PPA/pzqhf+GZ@zx2c4.com>
References: <20220520094459.116240-1-Jason@zx2c4.com>
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 <bbdeeca7-9c99-e661-6596-f04ea783a30b@kernel.dk>
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Hi Jens,

On Fri, May 20, 2022 at 09:34:46AM -0600, Jens Axboe wrote:
> On 5/20/22 9:25 AM, Jason A. Donenfeld wrote:
> > Hi Jens,
> > 
> > On Fri, May 20, 2022 at 11:44:56AM +0200, Jason A. Donenfeld wrote:
> >> Jens Axboe (3):
> >>   random: convert to using fops->read_iter()
> >>   random: convert to using fops->write_iter()
> >>   random: wire up fops->splice_{read,write}_iter()
> > 
> > FYI, this series makes reads from /dev/urandom slower, from around 616
> > MiB/s to 598 MiB/s on my system. That seems rather unfortunate.
> 
> How reproducible is that? That seems like a huge difference for the
> change. How big are the reads?

Fairly reproducible. Actually, if anything, it reproduces consistently
with worst results; I chose the most favorable ones for the new code.
This isn't any fancy `perf` profiling, but just running:

$ pv /dev/urandom > /dev/null

From looking at strace, the read size appears to be 131072.

Jason