On Thu, 2017-05-11 at 13:05 -0400, Boris Ostrovsky wrote: > On 05/11/2017 11:48 AM, Dario Faggioli wrote: > > > It probably would be at least a bit better, if scrub_free_pages() > > would > > check for softirqs() _before_ starting any scrubbing (which I don't > > think it does, right now, am I right?). > > Right. > > I didn't realize that do_tasklet() also schedules softirq. So you are > suggesting something along the lines of > > do_tasklet(); > > if ( !softirq_pending(smp_processor_id() && > !scrub_free_pages() ) > (*pm_idle)(); > > do_softirq(); > I was indeed suggesting something like that, and in fact I was about to say that, yes, what you wrote above should work.
*But* (and sorry for overlooking that), if there is more than one tasklet queued SCHEDULE_SOFTIRQ is not raised (look at the 'if (list_empty())' in do_tasklet()), and hence the softirq_pending() check would fail, and we'll still try to scrub. Basically, we'd have some scrubbing happening in between the processing of two tasklets (and this will repeat, as a pattern, if there are more than two), and unless someone else raises an (unrelated) softirq at some point, we may even scrub a significant amount of memory. So, it looks to me that the gating should consider both, softirq_pending() and tasklet_work_to_do (making it look really really similar to cpu_is_haltable()...). Regards, Dario -- <<This happens because I choose it to happen!>> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)
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