On Wed, Mar 04, 2020 at 04:22:41PM +0100, Karel Zak wrote: > On Wed, Mar 04, 2020 at 10:01:33AM +0800, Ian Kent wrote: > > On Tue, 2020-03-03 at 14:03 +0100, Greg Kroah-Hartman wrote: > > > Actually, I like this idea (the syscall, not just the unlimited > > > beers). > > > Maybe this could make a lot of sense, I'll write some actual tests > > > for > > > it now that syscalls are getting "heavy" again due to CPU vendors > > > finally paying the price for their madness... > > > > The problem isn't with open->read->close but with the mount info. > > changing between reads (ie. seq file read takes and drops the > > needed lock between reads at least once). > > readfile() is not reaction to mountinfo. > > The motivation is that we have many places with trivial > open->read->close for very small text files due to /sys and /proc. The > current way how kernel delivers these small strings to userspace seems > pretty inefficient if we can do the same by one syscall. > > Karel > > $ strace -e openat,read,close -c ps aux > ... > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 43.32 0.004190 4 987 read > 31.42 0.003039 3 844 4 openat > 25.26 0.002443 2 842 close > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.009672 2673 4 total > > $ strace -e openat,read,close -c lsns > ... > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 39.95 0.001567 2 593 openat > 30.93 0.001213 2 597 close > 29.12 0.001142 3 365 read > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.003922 1555 total > > > $ strace -e openat,read,close -c lscpu > ... > % time seconds usecs/call calls errors syscall > ------ ----------- ----------- --------- --------- ---------------- > 44.67 0.001480 7 189 52 openat > 34.77 0.001152 6 180 read > 20.56 0.000681 4 140 close > ------ ----------- ----------- --------- --------- ---------------- > 100.00 0.003313 509 52 total As a "real-world" test, would you recommend me converting one of the above tools to my implementation of readfile to see how/if it actually makes sense, or do you have some other tool you would rather see me try? thanks, greg k-h
