Messages in this thread | | | Subject | Re: [PATCH v4] rcu: Speed up calling of RCU tasks callbacks | From | Randy Dunlap <> | Date | Thu, 24 May 2018 16:26:38 -0700 |
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On 05/24/2018 04:22 PM, Steven Rostedt wrote: > On Thu, 24 May 2018 16:19:18 -0700 > Joel Fernandes <joel@joelfernandes.org> wrote: > >> On Thu, May 24, 2018 at 06:49:46PM -0400, Steven Rostedt wrote: >>> >>> From: Steven Rostedt (VMware) <rostedt@goodmis.org> >>> >>> 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. :-)
I think that you are confusing "drops it down to" with "drops it down by". You said the former. You should say the latter. IOW, I agree with Joel.
>> Other than minor change log change, looks good to me: >> >> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> > > Awesome, thanks! > > -- Steve >
-- ~Randy
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