linux-kernel - Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro

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Message-ID: <bbdeeca7-9c99-e661-6596-f04ea783a30b@kernel.dk>
Date:   Fri, 20 May 2022 09:34:46 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Theodore Ts'o <tytso@....edu>, Christoph Hellwig <hch@....de>,
        LKML <linux-kernel@...r.kernel.org>,
        Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro

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?

> Are we sure we really want to do this and need to do this?

I'm very sure, otherwise we're just accepting that we're breaking real
world applications. Alternatively, you can keep the ->read() and add the
->read_iter() as well, but I'm a bit skeptical at your initial results
there.

-- 
Jens Axboe