Eric Biggers <ebiggers3@xxxxxxxxx> wrote: > From: Eric Biggers <ebiggers@xxxxxxxxxx> > > 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: > > $ time ./stat_benchmark > > real 0m1.464s > user 0m0.275s > sys 0m1.187s > > $ time ./statx_benchmark > > real 0m5.530s > user 0m0.281s > sys 0m5.247s > > statx is expected to be a little slower than stat because struct statx > is larger than struct stat, but not by *that* much. It turns out that > most of the overhead was in copying struct statx to userspace, > apparently mostly in all the stac/clac instructions that got generated > for each __put_user() call. (This was on x86_64, but some other > architectures, e.g. arm64, have something similar now too.) > > stat() instead initializes its struct on the stack and copies it to > userspace with a single call to copy_to_user(). This turns out to be > much faster, and changing statx to do this makes it almost as fast as > stat: > > $ time ./statx_benchmark > > real 0m1.573s > user 0m0.229s > sys 0m1.344s > > Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx> Acked-by: David Howells <dhowells@xxxxxxxxxx>
