On Thu, Mar 07, 2019 at 11:36:18PM +0800, Coly Li wrote: > On 2019/3/7 11:06 下午, Shile Zhang wrote: > > > > On 2019/3/7 18:34, Coly Li wrote: > >> On 2019/3/7 1:15 下午, shile.zhang@xxxxxxxxxxxxxxxxx wrote: > >>> From: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx> > >>> > >>> Read /sys/fs/bcache/<uuid>/cacheN/priority_stats can take very long > >>> time with huge cache after long run. > >>> > >>> Signed-off-by: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx> > >> Hi Shile, > >> > >> Do you test your change ? It will be helpful with more performance data > >> (what problem that you improved). > > > > In case of 960GB SSD cache device, once read of the 'priority_stats' > > costs about 600ms in our test environment. > > > > After the fix, how much time it takes ? > > > > The perf tool shown that near 50% CPU time consumed by 'sort()', this > > means once sort will hold the CPU near 300ms. > > > > In our case, the statistics collector reads the 'priority_stats' > > periodically, it will trigger the schedule latency jitters of the > > > > task which shared same CPU core. > > > > Hmm, it seems you just make the sort slower, and nothing more changes. > Am I right ? Well, it has to make the sort slower, but it'll also avoid hogging the CPU (on a non-preemptible kernel), avoiding a potential soft lockup warning and allowing other tasks to run. -- Vojtech Pavlik VP SUSE Labs
