From: Richard Henderson <richard.henderson@linaro.org>
To: "Philippe Mathieu-Daudé" <f4bug@amsat.org>, qemu-devel@nongnu.org
Cc: Jason@zx2c4.com, sstabellini@kernel.org, pmatouse@redhat.com,
mst@redhat.com, sw@weilnetz.de, crosthwaite.peter@gmail.com,
mdroth@linux.vnet.ibm.com, pbonzini@redhat.com, pjp@redhat.com
Subject: Re: [Qemu-devel] [PATCH] tcg: Reduce max TB opcode count
Date: Fri, 15 Jun 2018 08:24:33 -1000 [thread overview]
Message-ID: <fc01b15d-538d-208a-7492-64f564bc2587@linaro.org> (raw)
In-Reply-To: <5351959f-75d4-014f-409e-d8a2a89bc433@amsat.org>
On 06/15/2018 03:58 AM, Philippe Mathieu-Daudé wrote:
> On 06/15/2018 03:25 AM, Richard Henderson wrote:
>> Also, assert that we don't overflow any of two different offsets into
>> the TB. Both unwind and goto_tb both record a uint16_t for later use.
>>
>> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
>> ---
>>
>> This fixes an arm-softmmu test case forwarded to me by Michael Tsirkin.
>>
>> There is a TB generated from that test case that runs to 7800 opcodes,
>> and compiles to 96k on an x64 host. This overflows the 16-bit offset
>> in which we record the goto_tb reset offset. Because of that overflow,
>> we install a jump destination that goes to neverland. Boom.
>>
>> With this reduced op count, the same TB compiles to about 48k for
>> both x64 and ppc64le hosts, and neither assertion fires.
>
> Why not keep that comment in the git history, to follow the 8k -> 4k change?
>
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Will do, thanks.
r~
prev parent reply other threads:[~2018-06-15 18:24 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-15 6:25 [Qemu-devel] [PATCH] tcg: Reduce max TB opcode count Richard Henderson
2018-06-15 13:44 ` Michael S. Tsirkin
2018-06-15 13:58 ` Philippe Mathieu-Daudé
2018-06-15 18:24 ` Richard Henderson [this message]
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