From: Peter Xu <peterx@redhat.com>
To: nsaenzju@redhat.com
Cc: linux-rt-users@vger.kernel.org, williams@redhat.com, jkacur@redhat.com
Subject: Re: [PATCH 2/3] oslat: Add aarch64 support
Date: Fri, 10 Sep 2021 09:33:04 -0400 [thread overview]
Message-ID: <YTtekExun9GoaFvc@t490s> (raw)
In-Reply-To: <6a2eba408dc4260a47c1acfe743474bb39aa93bd.camel@redhat.com>
On Fri, Sep 10, 2021 at 02:19:40PM +0200, nsaenzju@redhat.com wrote:
> > I also don't understand why you explicitly removed the compiler barrier. IIUC
> > when without it the compiler could move these instructions to be before/after
> > other instructions generated in the c code. That may not really happen in
> > practise, but just curious why the explicit removal.
>
> I removed it too as I see no justification for it. There is nothing, except for
> the actual timestamp values (which are safe as they come from an mrs), that
> could suffer from the compiler prefetching the value, or reordering accesses.
> I'll add a comment on the commit message.
Again I have no solid example, but wondering whether when without compiler
barrier the compiler would be legal to compile this code clip:
t1 = frc();
a = 1;
t2 = frc();
into something like:
t1 = frc();
t2 = frc();
a = 1;
It's just that iiuc compiler barrier has 0 overhead to us. No strong opinion
anyways.
--
Peter Xu
next prev parent reply other threads:[~2021-09-10 13:33 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-08 10:02 [PATCH 1/3] oslat: rename cpu_mhz/cpu_hz to timer_mhz/cpu_hz Nicolas Saenz Julienne
2021-09-08 10:02 ` [PATCH 2/3] oslat: Add aarch64 support Nicolas Saenz Julienne
2021-09-08 18:09 ` Peter Xu
2021-09-09 10:10 ` nsaenzju
2021-09-09 18:03 ` Peter Xu
2021-09-10 12:19 ` nsaenzju
2021-09-10 13:33 ` Peter Xu [this message]
2021-09-10 14:27 ` nsaenzju
2021-09-10 17:00 ` Peter Xu
2021-09-08 10:02 ` [PATCH 3/3] oslat: Allow for arch specific timer frequency measurements Nicolas Saenz Julienne
2021-09-08 18:16 ` Peter Xu
2021-09-09 10:29 ` nsaenzju
2021-09-09 18:04 ` Peter Xu
2021-09-08 14:40 ` [PATCH 1/3] oslat: rename cpu_mhz/cpu_hz to timer_mhz/cpu_hz Peter Xu
2021-09-08 16:30 ` nsaenzju
2021-09-08 17:51 ` Peter Xu
2021-09-09 9:41 ` nsaenzju
2021-09-09 18:05 ` Peter Xu
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