From: Segher Boessenkool <segher@kernel.crashing.org>
To: "Sven C. Dack" <sdack@gmx.com>
Cc: gcc-help@gcc.gnu.org
Subject: Re: L1/L2 cache characteristics and -mtune=znver2 versus run-time detection
Date: Wed, 16 Dec 2020 11:33:43 -0600 [thread overview]
Message-ID: <20201216173343.GK2672@gate.crashing.org> (raw)
In-Reply-To: <c6e0f4e3-18f9-4a2b-c502-a250383d97ed@gmx.com>
On Wed, Dec 16, 2020 at 04:30:00PM +0000, Sven C. Dack via Gcc-help wrote:
> Could some of the GCC experts please share their knowledge on this issue?
> >I've come across an unexpected behaviour of gcc and wanted to ask for
> >help. I've noticed that when I specify '-march=znver2' does gcc use the
> >incorrect values for the L1/L2 cache. Only when '-march=native' was used
> >and gcc detected the CPU at run-time does it use the correct values. For
> >example on a Ryzen 7 3800X (a Zen 2 CPU):
-march=native uses cpuid to get the cache info (or in general, looks at
the system it is running on). -march=znver2 does not. I do not know if
-march=znver2 should use better defaults.
> >Why does GCC not use the correct L1/L2 cache values when '-march=znver2'
> >or '-mtune=znver2' is specified?
Please open a PR? https://gcc.gnu.org/bugs.html . Thanks!
Segher
next prev parent reply other threads:[~2020-12-16 17:34 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-05 17:46 Sven C. Dack
2020-12-16 16:30 ` Sven C. Dack
2020-12-16 17:33 ` Segher Boessenkool [this message]
[not found] ` <3f4c127e-3cdd-5a4e-ef56-d5d62a88e30a@gmx.com>
[not found] ` <20201218101512.GQ2672@gate.crashing.org>
[not found] ` <20201218101912.GR2672@gate.crashing.org>
2020-12-18 13:32 ` Sven C. Dack
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