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From: Niek Linnenbank <nieklinnenbank@gmail.com>
To: Richard Henderson <richard.henderson@linaro.org>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
	qemu-arm <qemu-arm@nongnu.org>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"QEMU Developers" <qemu-devel@nongnu.org>,
	"Laurent Vivier" <laurent@vivier.eu>
Subject: Re: [PATCH v1 4/4] accel/tcg: increase default code gen buffer size for 64 bit
Date: Thu, 27 Feb 2020 20:07:24 +0100	[thread overview]
Message-ID: <CAPan3WrSRm986EfwJdXV2MduNLE5BS+QmCv0Bo5-BD+QfT-=dg@mail.gmail.com> (raw)
In-Reply-To: <56f5e355-9357-e212-e92b-9db1d8424dea@linaro.org>

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Hi Richard,

On Thu, Feb 27, 2020 at 1:57 PM Richard Henderson <
richard.henderson@linaro.org> wrote:

> On 2/27/20 4:31 AM, Alex Bennée wrote:
> >> It does not make sense for a linux-user chroot, running make -jN, on
> just about
> >> any host.  For linux-user, I could be happy with a modest increase, but
> not all
> >> the way out to 2GiB.
> >>
> >> Discuss.
> >
> > Does it matter that much? Surely for small programs the kernel just
> > never pages in the used portions of the mmap?
>
> That's why I used the example of a build under the chroot, because the
> compiler
> is not a small program.
>
> Consider when the memory *is* used, and N * 2GB implies lots of paging,
> where
> the previous N * 32MB did not.
>
> I agree that a lower default value probably is safer until we have more
proof that a larger value does not give any issues.


> I'm saying that we should consider a setting more like 128MB or so, since
> the
> value cannot be changed from the command-line, or through the environment.
>

Proposal: can we then introduce a new command line parameter for this?
Maybe in a new patch?
Since the size of the code generation buffer appears to have an impact on
performance,
in my opinion it would make sense to make it configurable by the user.

Regards,
Niek


>
>
> r~
>
>

-- 
Niek Linnenbank

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  parent reply	other threads:[~2020-02-27 19:08 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-26 18:10 [PATCH v1 0/4] Fix codegen translation cache size Alex Bennée
2020-02-26 18:10 ` [PATCH v1 1/4] accel/tcg: use units.h for defining code gen buffer sizes Alex Bennée
2020-02-26 22:00   ` Niek Linnenbank
2020-02-26 22:49   ` Richard Henderson
2020-02-27 10:54   ` Philippe Mathieu-Daudé
2020-02-26 18:10 ` [PATCH v1 2/4] accel/tcg: remove link between guest ram and TCG cache size Alex Bennée
2020-02-26 22:26   ` Niek Linnenbank
2020-02-26 22:50     ` Richard Henderson
2020-02-26 22:49   ` Richard Henderson
2020-02-27 10:58   ` Philippe Mathieu-Daudé
2020-02-26 18:10 ` [PATCH v1 3/4] accel/tcg: only USE_STATIC_CODE_GEN_BUFFER on 32 bit hosts Alex Bennée
2020-02-26 22:50   ` Richard Henderson
2020-02-27 10:55   ` Philippe Mathieu-Daudé
2020-02-27 19:20   ` Niek Linnenbank
2020-02-26 18:10 ` [PATCH v1 4/4] accel/tcg: increase default code gen buffer size for 64 bit Alex Bennée
2020-02-26 22:45   ` Niek Linnenbank
2020-02-27 12:19     ` Alex Bennée
2020-02-27 19:01       ` Niek Linnenbank
2020-02-26 22:55   ` Richard Henderson
2020-02-27 12:31     ` Alex Bennée
2020-02-27 12:56       ` Richard Henderson
2020-02-27 14:13         ` Igor Mammedov
2020-02-27 19:07         ` Niek Linnenbank [this message]
2020-02-28  7:47           ` Igor Mammedov
2020-02-28 19:20             ` Alex Bennée
2020-02-28  7:54         ` [PATCH] " Alex Bennée

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