On Wed, Jan 22, 2025 at 10:19:41PM +0300, Michael Tokarev wrote: > 08.01.2025 21:43, Daniel P. Berrangé пишет: > > We're seeing periodic reports of errors like: > > > > $ qemu-img create -f luks --object secret,data=123456,id=sec0 \ > > -o key-secret=sec0 luks-info.img 1M > > Formatting 'luks-info.img', fmt=luks size=1048576 key-secret=sec0 > > qemu-img: luks-info.img: Unable to get accurate CPU usage > > > > This error message comes from a recent attempt to workaround a > > kernel bug with measuring rusage in long running processes: > > > > commit c72cab5ad9f849bbcfcf4be7952b8b8946cc626e > > Author: Tiago Pasqualini <[email protected]> > > Date: Wed Sep 4 20:52:30 2024 -0300 > > > > crypto: run qcrypto_pbkdf2_count_iters in a new thread > > > > Unfortunately this has a subtle bug on machines which are very fast. > > > > On the first time around the loop, the 'iterations' value is quite > > small (1 << 15), and so will run quite fast. Testing has shown that > > some machines can complete this benchmarking task in as little as > > 7 milliseconds. > > > > Unfortunately the 'getrusage' data is not updated at the time of > > the 'getrusage' call, it is done asynchronously by the schedular. > > The 7 millisecond completion time for the benchmark is short > > enough that 'getrusage' sometimes reports 0 accumulated execution > > time. > > > > As a result the 'delay_ms == 0' sanity check in the above commit > > is triggering non-deterministically on such machines. > > > > The benchmarking loop intended to run multiple times, increasing > > the 'iterations' value until the benchmark ran for > 500 ms, but > > the sanity check doesn't allow this to happen. > > > > To fix it, we keep a loop counter and only run the sanity check > > after we've been around the loop more than 5 times. At that point > > the 'iterations' value is high enough that even with infrequent > > updates of 'getrusage' accounting data on fast machines, we should > > see a non-zero value. > > > > Reported-by: Thomas Huth <[email protected]> > > Reported-by: Richard W.M. Jones <[email protected]> > > Signed-off-by: Daniel P. Berrangé <[email protected]> > > Is this a qemu-stable material (9.2)?
Yes, please include it. With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
