On Thu, 24 May 2018 16:19:18 -0700 Joel Fernandes <[email protected]> wrote:
> On Thu, May 24, 2018 at 06:49:46PM -0400, Steven Rostedt wrote: > > > > From: Steven Rostedt (VMware) <[email protected]> > > > > Joel Fernandes found that the synchronize_rcu_tasks() was taking a > > significant amount of time. He demonstrated it with the following test: > > > > # cd /sys/kernel/tracing > > # while [ 1 ]; do x=1; done & > > # echo '__schedule_bug:traceon' > set_ftrace_filter > > # time echo '!__schedule_bug:traceon' > set_ftrace_filter; > > > > real 0m1.064s > > user 0m0.000s > > sys 0m0.004s > > > > Where it takes a little over a second to perform the synchronize, > > because there's a loop that waits 1 second at a time for tasks to get > > through their quiescent points when there's a task that must be waited > > for. > > > > After discussion we came up with a simple way to wait for holdouts but > > increase the time for each iteration of the loop but no more than a > > full second. > > > > With the new patch we have: > > > > # time echo '!__schedule_bug:traceon' > set_ftrace_filter; > > > > real 0m0.131s > > user 0m0.000s > > sys 0m0.004s > > > > Which drops it down to 13% of what the original wait time was. > > Should be 90% of original? That would be if I said "drops it down X" but I said "drops it down to X of what the original wait time was". And 0.131 is 13% of 1.064. :-) > Other than minor change log change, looks good to me: > > Reviewed-by: Joel Fernandes (Google) <[email protected]> Awesome, thanks! -- Steve
