linux-kernel - Re: [patch 0/9] x86_64: reliable TSC-based gettimeofday

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Message-ID: <20070201113440.GA26453@elte.hu>
Date:	Thu, 1 Feb 2007 12:34:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	jbohac@...e.cz
Cc:	Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.cz>, arjan@...radead.org,
	tglx@...utronix.de, johnstul@...ibm.com
Subject: Re: [patch 0/9] x86_64: reliable TSC-based gettimeofday


* jbohac@...e.cz <jbohac@...e.cz> wrote:

> This implementation allows the current time to be approximated by 
> reading the CPU's TSC even on SMP machines with unsynchronised TSCs. 
> This allows us to have a very fast gettimeofday() vsyscall on all SMP 
> machines supporting the RDTSCP instruction (AMD) or having 
> synchronised TSCs (Intel).
>
> Inter-CPU monotonicity can not, however, be guaranteed in a vsyscall, 
> so vsyscall is not used by default. Still, the syscall version of 
> gettimeofday is a lot faster using the TSC approximation instead of 
> other hardware timers.

ok, this looks mostly good to me - but this definitely should be based 
/ontop/ of the x86_64 GTOD code. I.e. ontop of these patches in -mm:

 generic-vsyscall-gtod-support-for-generic_time.patch
 generic-vsyscall-gtod-support-for-generic_time-tidy.patch
 time-x86_64-hpet_address-cleanup.patch
 revert-x86_64-mm-ignore-long-smi-interrupts-in-clock-calibration.patch
 time-x86_64-split-x86_64-kernel-timec-up.patch
 time-x86_64-split-x86_64-kernel-timec-up-tidy.patch
 time-x86_64-split-x86_64-kernel-timec-up-fix.patch
 reapply-x86_64-mm-ignore-long-smi-interrupts-in-clock-calibration.patch
 time-x86_64-convert-x86_64-to-use-generic_time.patch
 time-x86_64-convert-x86_64-to-use-generic_time-fix.patch
 time-x86_64-convert-x86_64-to-use-generic_time-tidy.patch
 time-x86_64-hpet-fixup-clocksource-changes.patch
 time-x86_64-tsc-fixup-clocksource-changes.patch
 time-x86_64-re-enable-vsyscall-support-for-x86_64.patch
 time-x86_64-re-enable-vsyscall-support-for-x86_64-tidy.patch

also, note that there is a new TSC synchronization check code in -mm as 
well:

 x86-rewrite-smp-tsc-sync-code.patch

this should be ontop of that too. (and ontop of the high-res timers 
queue)

	Ingo
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