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Re: [PATCH 6/6] aarch64: Add hp-timing.h
- From: pinskia at gmail dot com
- To: Andreas Schwab <schwab at suse dot de>
- 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 04:48:46 -0700
- Subject: Re: [PATCH 6/6] aarch64: Add hp-timing.h
- Authentication-results: sourceware.org; auth=none
- 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>
> 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.
Thanks,
Andrew
>
> Andreas.
>
> --
> Andreas Schwab, SUSE Labs, schwab@suse.de
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> "And now for something completely different."