From: Fabrice Bellard <fabrice@bellard.org>
To: qemu-devel@nongnu.org
Cc: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] [4600] variable dynamic translation buffer size
Date: Wed, 28 May 2008 17:11:33 +0200 [thread overview]
Message-ID: <483D7625.2030807@bellard.org> (raw)
In-Reply-To: <200805281355.53574.paul@codesourcery.com>
Paul Brook wrote:
> On Wednesday 28 May 2008, Fabrice Bellard wrote:
>> + code_gen_buffer = mmap(NULL, code_gen_buffer_size,
>> + PROT_WRITE | PROT_READ | PROT_EXEC,
>> + flags, -1, 0);
>
> I'd expect this to cause a significant performance regression on hosts that
> have limited branch range (i.e. everything except x86). The mmap region is
> almost never close to the application text segment, so all helper calls have
> to be indirect.
I knew that when I did the patch, but having a dynamic size on x86 hosts
prevails.
The other hosts can still implement hacks if they really need to, either
by reserving a huge data in BSS as it was done before or by using the
proc/x/maps entries to compute a possible mmap() address. IMHO I think
this is unnecessary as helpers should be the exception.
Fabrice.
next prev parent reply other threads:[~2008-05-28 15:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-05-28 12:30 [Qemu-devel] [4600] variable dynamic translation buffer size Fabrice Bellard
2008-05-28 12:55 ` Paul Brook
2008-05-28 15:11 ` Fabrice Bellard [this message]
2008-05-28 19:08 ` Blue Swirl
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