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

[Jason A. Donenfeld]

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