On Sat, Mar 11, 2017 at 06:16:55PM -0800, Eric Biggers wrote: > Hi Al, > > On Sun, Mar 12, 2017 at 01:24:15AM +0000, Al Viro wrote: > > On Sat, Mar 11, 2017 at 01:45:55PM -0800, Eric Biggers wrote: > > > From: Eric Biggers <ebigg...@google.com> > > > > > > I found that statx() was significantly slower than stat(). As a > > > microbenchmark, I compared 10,000,000 invocations of fstat() on a tmpfs > > > file to the same with statx() passed a NULL path: > > > > Umm... > > > > Well, it's a silly benchmark, but stat performance is important, and usually > things are cached already so most of the time is just overhead --- which this > measures. And since nothing actually uses statx() yet, you can't do a > benchmark > just by running some command like 'git status' or whatever.
Oh, I agree that multiple __put_user() are wrong; I also agree that bulk copy is the right approach (when we get the unsafe stuff right, we can revisit that, but I suspect that on quite a few architectures a bulk copy will still give better time, no matter what). > If padding is a concern at all (AFAICS it's not actually an issue now with > struct statx, but people tend to have different opinions on how careful they > want to be with padding), then I think we'll just have to start by memsetting > the whole struct to 0. My point is simply that it's worth a comment in that code.
