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References: <20190205151810.571-1-peter.maydell@linaro.org>
From: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <b8c414fe-e0cb-29ea-84cd-1f4386e6a10b@linaro.org>
Date: Wed, 6 Feb 2019 03:15:26 +0000
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Subject: Re: [Qemu-devel] [PATCH] accel/tcg: Consider cluster index in
 tb_lookup__cpu_state()
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To: Peter Maydell <peter.maydell@linaro.org>, qemu-devel@nongnu.org
Cc: patches@linaro.org, Howard Spoelstra <hsp.cat7@gmail.com>, Cleber Rosa <crosa@redhat.com>, =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= <philmd@redhat.com>, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>, Paolo Bonzini <pbonzini@redhat.com>, "Emilio G . Cota" <cota@braap.org>

On 2/5/19 3:18 PM, Peter Maydell wrote:
> In commit f7b78602fdc6c6e4be we added the CPU cluster number to the
> cflags field of the TB hash; this included adding it to the value
> kept in tb->cflags, since we pass that field directly into the hash
> calculation in some places. Unfortunately we forgot to check whether
> other parts of the code were doing comparisons against tb->cflags
> that would need to be updated.
> 
> It turns out that there is exactly one such place: the
> tb_lookup__cpu_state() function checks whether the TB it has
> found in the tb_jmp_cache has a tb->cflags matching the cf_mask
> that is passed in. The tb->cflags has the cluster_index in it
> but the cf_mask does not.
> 
> Hoist the "add cluster index to the cf_mask" code up from
> tb_htable_lookup() to tb_lookup__cpu_state() so it can be considered
> in the "did this TB match in the jmp cache" condition, as well as
> when we do the full hash lookup by physical PC, flags, etc.
> (tb_htable_lookup() is only called from tb_lookup__cpu_state(),
> so this change doesn't require any further knock-on changes.)
> 
> Fixes: f7b78602fdc6c6e4be ("accel/tcg: Add cluster number to TCG TB hash")
> Reported-by: Howard Spoelstra <hsp.cat7@gmail.com>
> Reported-by: Cleber Rosa <crosa@redhat.com>
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>

> Does anybody know why tb_lookup__cpu_state() has that odd
> double-underscore in the middle of its name?

I'm inclined to think typo...  Emilio?


r~