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Date: Sat, 13 Jun 2015 10:48:40 +0200 From: Borislav Petkov <bp@...e.de> To: Andy Lutomirski <luto@...capital.net> Cc: Thomas Gleixner <tglx@...utronix.de>, John Stultz <john.stultz@...aro.org>, Aaron Lu <aaron.lu@...el.com>, X86 ML <x86@...nel.org>, Tony Li <tony.li@....com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Suravee Suthikulanit <suravee.suthikulpanit@....com>, Frédéric Weisbecker <fweisbec@...il.com>, Fengguang Wu <fengguang.wu@...el.com>, Len Brown <lenb@...nel.org>, Ken Xue <ken.xue@....com>, Huang Rui <ray.huang@....com>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Peter Zijlstra <peterz@...radead.org> Subject: Re: [PATCH v2 3/4] x86, mwaitt: introduce mwaix delay with a configurable timer On Fri, Jun 12, 2015 at 04:15:23PM -0700, Andy Lutomirski wrote: > > How about this: > > > > /* > > * This should be a memory location in a cache line which is > > * unlikely to be touched by other processors. The actual > > * content is immaterial as it is not actually modified in any way. > > */ > > mwait_ptr = ¤t_thread_info()->flags; > > > > and then > > > > __monitor(mwait_ptr, 0, 0); > > > > We already do this in mwait_play_dead(). > > > > However, am I even correct in assuming that ->flags won't really be > > touched as we're doing delay() and nothing pokes into current anyway? > > We poke flags remotely, but not frequently enough for this to be a > problem. However, I don't know that touching current in udelay is > okay. > > How about some read-mostly percpu variable, such as cpu_tss? Yeah, those look much safer since they're static and are ____cacheline_aligned_in_smp, which is exactly what we want. I guess we can do __monitorx(this_cpu_ptr(&cpu_tss), 0, 0); with a nice comment ontop why we're doing it. asm looks ok too: movq $cpu_tss, %rax #, tcp_ptr__ add %gs:this_cpu_off(%rip), %rax # this_cpu_off, tcp_ptr__ xorl %edx, %edx # tmp248 movq %rdx, %rcx # tmp248, tmp248 #APP # 22 "./arch/x86/include/asm/mwait.h" 1 .byte 0x0f, 0x01, 0xc8; # 0 "" 2 #NO_APP Thanks. -- Regards/Gruss, Boris. ECO tip #101: Trim your mails when you reply. -- -- 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/
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