From: Richard Henderson <rth@twiddle.net>
To: Paolo Bonzini <pbonzini@redhat.com>,
vijay.kilari@gmail.com, qemu-arm@nongnu.org,
peter.maydell@linaro.org
Cc: qemu-devel@nongnu.org, Vijaya Kumar K <Vijaya.Kumar@cavium.com>
Subject: Re: [Qemu-devel] [PATCH v3 3/3] utils: Add prefetch for Thunderx platform
Date: Mon, 24 Oct 2016 08:51:52 -0700 [thread overview]
Message-ID: <cbdd5daf-41db-a897-8bbd-9558adb90011@twiddle.net> (raw)
In-Reply-To: <538a5505-fef3-fc2b-4411-bbaa8537c9c7@redhat.com>
On 10/24/2016 04:25 AM, Paolo Bonzini wrote:
>> > for (; p + 8 <= e; p += 8) {
>> > - __builtin_prefetch(p + 8, 0, 0);
>> > + __builtin_prefetch(p +
>> > + (8 * cache_line_factor * prefetch_line_dist), 0, 0);
> You should precompute cache_line_bytes * prefetch_line_dist /
> sizeof(uint64_t) in a single variable, prefetch_distance. This saves
> the effort of loading global variables repeatedly. Then you can do
>
> __builtin_prefetch(p + prefetch_distance, 0, 0);
>
Let's not complicate things by dividing by sizeof(uint64_t).
It's less complicated to avoid both that and the implied multiply.
__builtin_prefetch((char *)p + prefetch_distance, 0, 0)
r~
next prev parent reply other threads:[~2016-10-24 16:06 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-24 5:55 [Qemu-devel] [PATCH v3 0/3] Live migration optimization for Thunderx platform vijay.kilari
2016-10-24 5:55 ` [Qemu-devel] [PATCH v3 1/3] cutils: Set __builtin_prefetch optional parameters vijay.kilari
2016-10-24 15:43 ` Richard Henderson
2016-10-24 5:55 ` [Qemu-devel] [PATCH v3 2/3] utils: Add helper to read arm MIDR_EL1 register vijay.kilari
2016-10-24 9:39 ` Dr. David Alan Gilbert
2016-10-24 10:20 ` Vijay Kilari
2016-10-24 11:26 ` Paolo Bonzini
2016-10-24 15:47 ` Richard Henderson
2016-10-24 5:55 ` [Qemu-devel] [PATCH v3 3/3] utils: Add prefetch for Thunderx platform vijay.kilari
2016-10-24 11:25 ` Paolo Bonzini
2016-10-24 15:51 ` Richard Henderson [this message]
2016-10-24 15:47 ` [Qemu-devel] [PATCH v3 0/3] Live migration optimization " Richard Henderson
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