Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <bbdeeca7-9c99-e661-6596-f04ea783a30b@kernel.dk>
Date:   Fri, 20 May 2022 09:34:46 -0600
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:91.0) Gecko/20100101
 Thunderbird/91.8.1
Subject: Re: [PATCH v4 0/3] random: convert to using iters, for Al Viro
Content-Language: en-US
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Theodore Ts'o <tytso@mit.edu>, Christoph Hellwig <hch@lst.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Al Viro <viro@zeniv.linux.org.uk>
References: <20220520094459.116240-1-Jason@zx2c4.com>
 <Yoey+FOYO69lS5qP@zx2c4.com>
From:   Jens Axboe <axboe@kernel.dk>
In-Reply-To: <Yoey+FOYO69lS5qP@zx2c4.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

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