Re: [Qemu-devel] [PATCH 1/8] tcg: Clean up direct block chaining data fields

From: Paolo Bonzini <pbonzini@redhat.com>
To: "Richard Henderson" <rth@twiddle.net>,
	"Alex Bennée" <alex.bennee@linaro.org>,
	"Sergey Fedorov" <serge.fdrv@gmail.com>
Cc: sergey.fedorov@linaro.org,
	Peter Crosthwaite <crosthwaite.peter@gmail.com>,
	Stefan Weil <sw@weilnetz.de>,
	Claudio Fontana <claudio.fontana@huawei.com>,
	qemu-devel@nongnu.org, Alexander Graf <agraf@suse.de>,
	Blue Swirl <blauwirbel@gmail.com>,
	qemu-arm@nongnu.org, "Vassili Karpov (malc)" <av1474@comtv.ru>,
	Aurelien Jarno <aurelien@aurel32.net>
Subject: Re: [Qemu-devel] [PATCH 1/8] tcg: Clean up direct block chaining data fields
Date: Tue, 29 Mar 2016 10:51:28 +0200	[thread overview]
Message-ID: <56FA4210.20707@redhat.com> (raw)
In-Reply-To: <56FA3981.60608@redhat.com>

On 29/03/2016 10:14, Paolo Bonzini wrote:
> 
> 
> On 29/03/2016 00:12, Richard Henderson wrote:
>>> There is also a case where a TB jumps to itself; it then appears twice
>>> in the list with different values in the low bits, such as this:
>>>
>>>      tb->jmp_list_first = tb | 0;
>>>       .--------------------'   |
>>>       |                .-------'
>>>      tb->jmp_list_next[0] = tb | 2;
>>
>> Of course, it begs the question of why TB would be in its own list, even
>> if it does jump to itself.  We only need the points-to list in order to
>> invalidate a TB and unlink it.  But if TB is being invalidated, we don't
>> need to reset the jump within TB itself.
> 
> Isn't it just because TB acts as the list head in the circular list?  Or
> am I misunderstanding you?

Ok, that was dumb. :) Understood it now.

Paolo