From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37624) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1dUJlT-0003UL-1W for qemu-devel@nongnu.org; Sun, 09 Jul 2017 17:29:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1dUJlP-0004xV-UF for qemu-devel@nongnu.org; Sun, 09 Jul 2017 17:29:15 -0400 Received: from out3-smtp.messagingengine.com ([66.111.4.27]:45941) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1dUJlP-0004xC-In for qemu-devel@nongnu.org; Sun, 09 Jul 2017 17:29:11 -0400 Date: Sun, 9 Jul 2017 17:29:10 -0400 From: "Emilio G. Cota" Message-ID: <20170709212910.GA3027@flamenco> References: <1499586614-20507-1-git-send-email-cota@braap.org> <1499586614-20507-22-git-send-email-cota@braap.org> <3fabc9d4-86b5-9d01-9499-3468bd2f2e5e@twiddle.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <3fabc9d4-86b5-9d01-9499-3468bd2f2e5e@twiddle.net> Subject: Re: [Qemu-devel] [PATCH 21/22] tcg: enable per-thread TCG for softmmu List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Richard Henderson Cc: qemu-devel@nongnu.org On Sun, Jul 09, 2017 at 11:19:37 -1000, Richard Henderson wrote: > On 07/08/2017 09:50 PM, Emilio G. Cota wrote: > >This allows us to generate TCG code in parallel. MTTCG already uses > >it, although the next commit pushes down a lock to actually > >perform parallel generation. > > > >User-mode is kept out of this: contention due to concurrent translation > >is more commonly found in full-system mode. > > Um, why do you believe that? Are you suggesting that a multi-threaded > user-only guest is much more likely to share TBs and do much less code > generation total? Exactly. Also, in user-mode "vCPU threads" (i.e. host threads) come and go all the time, so this doesn't work well with having a single code_gen_buffer, which I assumed was non-negotiable. > At the moment I think it's just a confusing distinction. As proven by some > of the comment adjustments you made. > > >-TCGContext tcg_ctx; > >+TCG_THREAD TCGContext tcg_ctx; > > This is a really large structure, and it's not needed by any of the I/O > threads. We're probably better off dynamically allocating this ourselves > and do something like (snip) Agreed, will look into this. E.