From: "Jan Beulich" <JBeulich@suse.com>
To: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: Xen-devel <xen-devel@lists.xen.org>
Subject: Re: [PATCH] x86/emul: Calculate not_64bit during instruction decode
Date: Mon, 16 Jan 2017 05:50:37 -0700 [thread overview]
Message-ID: <587CCFAD0200007800130725@prv-mh.provo.novell.com> (raw)
In-Reply-To: <1484563769-14726-1-git-send-email-andrew.cooper3@citrix.com>
>>> On 16.01.17 at 11:49, <andrew.cooper3@citrix.com> wrote:
> ... rather than repeating "generate_exception_if(mode_64bit(), EXC_UD);" in
> the emulation switch statement.
>
> Bloat-o-meter shows:
>
> add/remove: 0/0 grow/shrink: 1/2 up/down: 8/-495 (-487)
> function old new delta
> per_cpu__state 98 106 +8
> x86_decode 6782 6726 -56
> x86_emulate 57160 56721 -439
>
> The reason for x86_decode() getting smaller is that this change alters the
> x86_decode_onebyte() switch statement from a chain of if()/else's to a jump
> table. The jump table adds 250 bytes of data which bloat-o-meter clearly
> can't see.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
> I am also considering doing similar for vcpu cpuid checks, to split apart the
> logic deciding on the feature to check from the emulation logic. This will
> simplify some of the larger blocks, especially the mov emulation.
Not sure about this one, specifically also in the context of the
SSEn/AVX support work I'm doing right now (where individual insn
variants have different CPUID dependencies).
Jan
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prev parent reply other threads:[~2017-01-16 12:50 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-16 10:49 [PATCH] x86/emul: Calculate not_64bit during instruction decode Andrew Cooper
2017-01-16 12:50 ` Jan Beulich [this message]
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