On Wed, 23 Mar 2022 at 23:20, Theodore Ts'o <tytso@xxxxxxx> wrote: > > On Wed, Mar 23, 2022 at 02:24:40PM +0100, Miklos Szeredi wrote: > > The reason I stated thinking about this is that Amir wanted a per-sb > > iostat interface and dumped it into /proc/PID/mountstats. And that is > > definitely not the right way to go about this. > > > > So we could add a statfsx() and start filling in new stuff, and that's > > what Linus suggested. But then we might need to add stuff that is not > > representable in a flat structure (like for example the stuff that > > nfs_show_stats does) and that again needs new infrastructure. > > > > Another example is task info in /proc. Utilities are doing a crazy > > number of syscalls to get trivial information. Why don't we have a > > procx(2) syscall? I guess because lots of that is difficult to > > represent in a flat structure. Just take the lsof example: tt's doing > > hundreds of thousands of syscalls on a desktop computer with just a > > few hundred processes. > > I'm still a bit puzzled about the reason for getvalues(2) beyond, > "reduce the number of system calls". Is this a performance argument? One argument that can't be worked around without batchingis atomicity. Not sure how important that is, but IIRC it was one of the requirements relating to the proposed fsinfo syscall, which this API is meant to supersede. Performance was also oft repeated regarding the fsinfo API, but I'm less bought into that. > If so, have you benchmarked lsof using this new interface? Not yet. Looked yesterday at both lsof and procps source code, and both are pretty complex and not easy to plug in a new interface. But I've not yet given up... > I did a quickie run on my laptop, which currently had 444 process. > "lsof /home/tytso > /tmp/foo" didn't take long: > > % time lsof /home/tytso >& /tmp/foo > real 0m0.144s > user 0m0.039s > sys 0m0.087s > > And an strace of that same lsof command indicated had 67,889 lines. > So yeah, lots of system calls. But is this new system call really > going to speed up things by all that much? $ ps uax | wc -l 335 $ time lsof > /dev/null real 0m3.011s user 0m1.257s sys 0m1.249s $ strace -o /tmp/strace lsof > /dev/null $ wc -l /tmp/strace 638523 /tmp/strace That's an order of magnitude higher than in your case; don't know what could cause this. Thanks, Millos
