From: Aurelien Jarno <aurelien@aurel32.net>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Alexander Graf <agraf@suse.de>,
Paolo Bonzini <pbonzini@redhat.com>,
qemu-ppc@nongnu.org, qemu-devel@nongnu.org,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH v3] tcg/ppc: Improve unaligned load/store handling on 64-bit backend
Date: Tue, 21 Jul 2015 17:29:12 +0200 [thread overview]
Message-ID: <20150721152912.GA30591@aurel32.net> (raw)
In-Reply-To: <1437455978.5809.2.camel@kernel.crashing.org>
On 2015-07-21 15:19, Benjamin Herrenschmidt wrote:
> Currently, we get to the slow path for any unaligned access in the
> backend, because we effectively preserve the bottom address bits
> below the alignment requirement when comparing with the TLB entry,
> so any non-0 bit there will cause the compare to fail.
>
> For the same number of instructions, we can instead add the access
> size - 1 to the address and stick to clearing all the bottom bits.
>
> That means that normal unaligned accesses will not fallback (the HW
> will handle them fine). Only when crossing a page boundary well we
> end up having a mismatch because we'll end up pointing to the next
> page which cannot possibly be in that same TLB entry.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
--
Aurelien Jarno GPG: 4096R/1DDD8C9B
aurelien@aurel32.net http://www.aurel32.net
next prev parent reply other threads:[~2015-07-21 15:29 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-21 5:19 [Qemu-devel] [PATCH v3] tcg/ppc: Improve unaligned load/store handling on 64-bit backend Benjamin Herrenschmidt
2015-07-21 6:27 ` Richard Henderson
2015-07-21 6:33 ` Benjamin Herrenschmidt
2015-07-21 6:39 ` Richard Henderson
2015-07-21 9:46 ` Benjamin Herrenschmidt
2015-07-21 12:04 ` Alexander Graf
2015-07-21 12:26 ` Benjamin Herrenschmidt
2015-07-21 13:48 ` Paolo Bonzini
2015-07-21 14:18 ` Alexander Graf
2015-07-21 21:09 ` Benjamin Herrenschmidt
2015-07-21 21:06 ` Benjamin Herrenschmidt
2015-07-21 15:30 ` Aurelien Jarno
2015-07-21 15:29 ` Aurelien Jarno [this message]
2015-07-24 12:34 ` Richard Henderson
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