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Re: [PATCH 6/6] aarch64: Add hp-timing.h
- From: Andreas Schwab <schwab at suse dot de>
- To: pinskia at gmail dot com
- Cc: Richard Henderson <rth at twiddle dot net>, "libc-alpha\ at sourceware dot org" <libc-alpha at sourceware dot org>, "azanella\ at linux dot vnet dot ibm dot com" <azanella at linux dot vnet dot ibm dot com>, "davem\ at davemloft dot net" <davem at davemloft dot net>, "marcus dot shawcroft\ at arm dot com" <marcus dot shawcroft at arm dot com>
- Date: Mon, 21 Jul 2014 14:01:32 +0200
- Subject: Re: [PATCH 6/6] aarch64: Add hp-timing.h
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- References: <1403735086-21797-1-git-send-email-rth at twiddle dot net> <1403735086-21797-7-git-send-email-rth at twiddle dot net> <mvmd2czlz0k dot fsf at hawking dot suse dot de> <812AFAEE-C8E5-4583-8647-7E5ABE02F95C at gmail dot com>
pinskia@gmail.com writes:
>> On Jul 21, 2014, at 4:41 AM, Andreas Schwab <schwab@suse.de> wrote:
>>
>> Richard Henderson <rth@twiddle.net> writes:
>>
>>> +/* Sync the instruction stream, and read from the virtual cycle counter. */
>>> +#define HP_TIMING_NOW(Var) \
>>> + __asm__ __volatile__ ("isb; mrs %0, cntvct_el0" : "=r" (Var))
>>
>> According to https://bugs.launchpad.net/bugs/1344320 the generic timers
>> are not part of the kernel-to-userspace contract.
>
>
> I think this is bogus for the kernel folks not allow a high precision timer in user space. Timers like this are needed for micro-benchmarking compiler changes along with other libc changes.
According to the qemu bug the timers are optional.
Andreas.
--
Andreas Schwab, SUSE Labs, schwab@suse.de
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