Date: Thu, 26 Aug 2010 15:24:37 -0700 From: mdf@FreeBSD.org To: Andriy Gapon <avg@icyb.net.ua> Cc: freebsd-current@freebsd.org Subject: Re: sched_pin() bug in SCHED_ULE Message-ID: <AANLkTi=fo2LiGm8rhffTd8rPryq7b1doQdVihmL0YMdT@mail.gmail.com> In-Reply-To: <4C76E661.60600@icyb.net.ua> References: <AANLkTin6V9pc3d7ifyOmR2V-H5-g_AQFji-LbZzWfAKM@mail.gmail.com> <201008261649.20543.jhb@freebsd.org> <AANLkTi=7cLfH3h3jMVhbEzNsuiPod3Zx=PiazK7Dn4%2BA@mail.gmail.com> <4C76E661.60600@icyb.net.ua>
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On Thu, Aug 26, 2010 at 3:10 PM, Andriy Gapon <avg@icyb.net.ua> wrote: > on 27/08/2010 00:20 mdf@FreeBSD.org said the following: >> >> I tried making sched_pin() a real function which used >> intr_disable/intr_restore around saving off td->td_oncpu, >> td->td_lastcpu and ts->ts_cpu, and the stack at the time of call. In >> sched_switch when I saw an unexpected migration I printed all that >> out. I found that on my boxes, at sched_pin() time ts_cpu was already >> different from td->td_oncpu, so the specific problem I was having was >> that while another thread can change ts_cpu it has no way to force >> that thread to immediately migrate. > > Like e.g. in sched_affinity where ts_cpu is first changed and then the old cpu > is ipi-ed? That could do it. I didn't follow the stack of the places that were touching ts_cpu for non-curthread. >> I believe the below patch fixes the issue, though I'm open to other methods: >> >> >> Index: kern/sched_ule.c >> =================================================================== >> --- kern/sched_ule.c (.../head/src/sys) (revision 158279) >> +++ kern/sched_ule.c (.../branches/BR_BUG_67957/src/sys) (revision 158279) >> @@ -112,6 +112,7 @@ >> /* flags kept in ts_flags */ >> #define TSF_BOUND 0x0001 /* Thread can not migrate. */ >> #define TSF_XFERABLE 0x0002 /* Thread was added as transferable. */ >> +#define TSF_BINDING 0x0004 /* Thread is being bound. */ > > I don't really follow why TSF_BINDING is needed, i.e. why TSF_BOUND is not > sufficient in this case? I wanted to tighten up the asserts, so that the only time it was okay for a td_pinned thread to migrate was the one time it was moving to the target cpu. Having a separate flag allows that. Thanks, matthew
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