From: Michael Ellerman <mpe@ellerman.id.au> To: Shreyas B Prabhu <shreyas@linux.vnet.ibm.com> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>, linux-kernel@vger.kernel.org, Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org Subject: Re: [RFC, v2] powerpc/powernv: Introduce kernel param to control fastsleep workaround behavior Date: Wed, 18 Mar 2015 15:55:59 +1100 [thread overview] Message-ID: <1426654559.6504.3.camel@ellerman.id.au> (raw) In-Reply-To: <55084D0C.1040309@linux.vnet.ibm.com> On Tue, 2015-03-17 at 21:19 +0530, Shreyas B Prabhu wrote: > > On Tuesday 17 March 2015 03:09 PM, Benjamin Herrenschmidt wrote: > > On Tue, 2015-03-17 at 19:57 +1100, Michael Ellerman wrote: > >> > >> >From what I can see below, the decision as to whether you apply the workaround > >> or not doesn't affect the list of idle states. So this could just as well be a > >> runtime parameter, ie. a sysfs file, which can then be set by the user whenever > >> they like? They might do it in a boot script, but that's up to them. > > > > Right, that would work too. > > Okay. I'll send a patch with this design. Thanks. > >> For simplicity I think it would also be fine to make it a write-once parameter, > >> ie. you don't need to handle undoing it. > > > > It would be easy enough to make it rw using stop machine I think... > > > >> I think the only complication that would add is that you'd need to be a little > >> careful about the order in which you nop out the calls vs applying the > >> workaround, in case some threads are idle when you're called. > > Right, we should be safe with this sequence- > - NOP call to undo workaround > - Apply workaround on all cores. > - NOP call to apply workaround Yeah that sounds right. > > I wouldn't bother with NOP'ing in that case, a runtime test will probably be noise > > in the measurement. > > Didn't get your point here. Do you mean, ignore the request if some > cores are in sleep or deeper state? I *think* what he means is we probably don't actually need to patch a nop in/out. Instead we could just test a flag, because the cost of testing a flag is miniscule compared to the rest of the logic. cheers
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From: Michael Ellerman <mpe@ellerman.id.au> To: Shreyas B Prabhu <shreyas@linux.vnet.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras <paulus@samba.org>, linux-kernel@vger.kernel.org Subject: Re: [RFC, v2] powerpc/powernv: Introduce kernel param to control fastsleep workaround behavior Date: Wed, 18 Mar 2015 15:55:59 +1100 [thread overview] Message-ID: <1426654559.6504.3.camel@ellerman.id.au> (raw) In-Reply-To: <55084D0C.1040309@linux.vnet.ibm.com> On Tue, 2015-03-17 at 21:19 +0530, Shreyas B Prabhu wrote: > > On Tuesday 17 March 2015 03:09 PM, Benjamin Herrenschmidt wrote: > > On Tue, 2015-03-17 at 19:57 +1100, Michael Ellerman wrote: > >> > >> >From what I can see below, the decision as to whether you apply the workaround > >> or not doesn't affect the list of idle states. So this could just as well be a > >> runtime parameter, ie. a sysfs file, which can then be set by the user whenever > >> they like? They might do it in a boot script, but that's up to them. > > > > Right, that would work too. > > Okay. I'll send a patch with this design. Thanks. > >> For simplicity I think it would also be fine to make it a write-once parameter, > >> ie. you don't need to handle undoing it. > > > > It would be easy enough to make it rw using stop machine I think... > > > >> I think the only complication that would add is that you'd need to be a little > >> careful about the order in which you nop out the calls vs applying the > >> workaround, in case some threads are idle when you're called. > > Right, we should be safe with this sequence- > - NOP call to undo workaround > - Apply workaround on all cores. > - NOP call to apply workaround Yeah that sounds right. > > I wouldn't bother with NOP'ing in that case, a runtime test will probably be noise > > in the measurement. > > Didn't get your point here. Do you mean, ignore the request if some > cores are in sleep or deeper state? I *think* what he means is we probably don't actually need to patch a nop in/out. Instead we could just test a flag, because the cost of testing a flag is miniscule compared to the rest of the logic. cheers
next prev parent reply other threads:[~2015-03-18 4:56 UTC|newest] Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-03-17 4:13 [PATCH RFC v2] powerpc/powernv: Introduce kernel param to control fastsleep workaround behavior Shreyas B. Prabhu 2015-03-17 4:13 ` Shreyas B. Prabhu 2015-03-17 8:57 ` [RFC, " Michael Ellerman 2015-03-17 9:39 ` Benjamin Herrenschmidt 2015-03-17 9:39 ` Benjamin Herrenschmidt 2015-03-17 15:49 ` Shreyas B Prabhu 2015-03-17 15:49 ` Shreyas B Prabhu 2015-03-18 4:55 ` Michael Ellerman [this message] 2015-03-18 4:55 ` Michael Ellerman
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