From: Jisheng Zhang <jszhang@kernel.org>
To: Ben Dooks <ben.dooks@codethink.co.uk>
Cc: linux-riscv@lists.infradead.org,
PalmerDabbelt <palmer@dabbelt.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Albert Ou <aou@eecs.berkeley.edu>, Evan Green <evan@rivosinc.com>
Subject: Re: boot time regressed a lot due to misaligned access probe
Date: Wed, 13 Sep 2023 23:11:12 +0800 [thread overview]
Message-ID: <ZQHREHx4XCN70iUq@xhacker> (raw)
In-Reply-To: <17d351c6-e6c3-43ce-a466-691778ba05c3@codethink.co.uk>
On Wed, Sep 13, 2023 at 11:46:28AM +0100, Ben Dooks wrote:
> On 13/09/2023 01:14, Jisheng Zhang wrote:
> > Hi all,
> >
> > Probing one cpu for misaligned access cost about 0.06s, so it will cost
> > about 3.8s on platforms with 64 CPUs, for example, milkv pioneer which
> > is powered by sg2042.
> >
> > I'm not sure the reason of probing misaligned access for all CPUs. If
> > the HW doesn't behave as SMP from misalligned access side, then unless
> > userspace processes force cpu affinity, they always suffer from this
> > non-SMP pain.
> >
> > So, can we only probe the boot cpu?
>
> So a couple of ideas:
>
> #1 is it worth adding a device-tree property to explicitly to say if
> the unaligned access has been measured and known
>
> #2 only probe one cpu in a cluster if there are multiple clusters of
> cpus?
and #3 Could userspace who cares about misaligned access probe the
speed itself? And this reminds me the arm case: old armv5te VS armv7,
there's no such probe in arm yet.
>
> --
> Ben Dooks http://www.codethink.co.uk/
> Senior Engineer Codethink - Providing Genius
>
> https://www.codethink.co.uk/privacy.html
>
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next prev parent reply other threads:[~2023-09-13 15:23 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-13 0:14 boot time regressed a lot due to misaligned access probe Jisheng Zhang
2023-09-13 10:46 ` Ben Dooks
2023-09-13 15:11 ` Jisheng Zhang [this message]
2023-09-13 19:50 ` Evan Green
2023-09-13 19:53 ` Palmer Dabbelt
2023-09-15 0:55 ` Jisheng Zhang
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