lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
Open Source and information security mailing list archives
| ||
|
Date: Mon, 3 Aug 2015 16:11:52 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Frederic Weisbecker <fweisbec@...il.com> Cc: LKML <linux-kernel@...r.kernel.org>, Thomas Gleixner <tglx@...utronix.de>, Preeti U Murthy <preeti@...ux.vnet.ibm.com>, Christoph Lameter <cl@...ux.com>, Ingo Molnar <mingo@...nel.org>, Viresh Kumar <viresh.kumar@...aro.org>, Rik van Riel <riel@...hat.com> Subject: Re: [PATCH 05/10] nohz: New tick dependency mask On Mon, Aug 03, 2015 at 03:55:34PM +0200, Frederic Weisbecker wrote: > On Mon, Aug 03, 2015 at 03:29:58PM +0200, Peter Zijlstra wrote: > > On Mon, Aug 03, 2015 at 03:09:39PM +0200, Frederic Weisbecker wrote: > > > > > > That doesn't make any sense: > > > > > > > > tick_nohz_set_tick_dependency_this_cpu(); > > > > > > > > (shees, you're nowhere near lazy enough, that's insane to type) is > > > > almost identical to: > > > > > > > > tick_nohz_set_tick_dependency_cpu(.cpu = smp_processor_id()); > > > > > > > > The only difference is a _very_ slight reduction in cost for computing > > > > the per-cpu offset. > > > > > > But the local one must be NMI-safe. Now I can do: > > > > > > if (cpu == smp_processor_id()) > > > tick_nohz_full_kick() // NMI-safe > > > else > > > tick_nohz_full_kick_cpu(cpu); // not NMI-safe. > > > > Urgh, I missed that. But yes, I suppose that's ok seeing how we result > > in a smaller interface. > > > > I was going to say that with a bit of luck GCC could optimize it, but > > its not inline so no it cannot. > > I might inline all these set_dep() things to introduce static keys on these > APIs.. But the kick itself will remain real calls. Sure, but first check if GCC will optimize: static inline void foo(int cpu) { if (cpu == smp_processor_id()) bar1(); else bar2(); } foo(smp_processor_id()); Into a direct call to bar1(), if not see if we can make it so. If not, there's no point in inlining at all. > Ok how about tick_nohz_set_dep_nmi() so that we know exactly what's the purpose > here. Still a long function name but it's clear. Only for the set, if you really care about it. The alternative is WARN_ON(in_nmi() && cpu != smp_processor_id()) or somesuch. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists