On Sun, Sep 06, 2020 at 08:38:20PM +0200, Pavel Machek wrote: > On Sun 2020-09-06 20:35:38, Christophe Leroy wrote: > > Hi, > > > > Le 06/09/2020 à 20:21, Pavel Machek a écrit : > > >Hi! > > > > > >>>>Christophe reported a major speedup due to avoiding the iov_iter > > >>>>overhead, so just add this trivial function. Note that /dev/zero > > >>>>already implements both an iter and non-iter writes so this just > > >>>>makes it more symmetric. > > >>>> > > >>>>Christophe Leroy <christophe.le...@csgroup.eu> > > >>>>Signed-off-by: Christoph Hellwig <h...@lst.de> > > >>> > > >>>Tested-by: Christophe Leroy <christophe.le...@csgroup.eu> > > >> > > >>Any idea what has happened to make the 'iter' version so bad? > > > > > >Exactly. Also it would be nice to note how the speedup was measured > > >and what the speedup is. > > > > > > > Was measured on an 8xx powerpc running at 132MHz with: > > > > dd if=/dev/zero of=/dev/null count=1M > > > > With the patch, dd displays a throughput of 113.5MB/s > > Without the patch it is 99.9MB/s > > Actually... that does not seem like a huge deal. read(/dev/zero) is > not that common operation.
There is nothing wrong with this patch (aside from the sparse warning), and it's in my tree now, so I don't understand complaining about it... greg k-h
