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[97.126.123.70]) by smtp.gmail.com with ESMTPSA id d4sm7178468pjg.19.2020.01.30.08.09.40 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 30 Jan 2020 08:09:41 -0800 (PST) Subject: Re: [PATCH 0/4] target/ppc: Use probe_access To: Aleksandar Markovic References: <20200129235040.24022-1-richard.henderson@linaro.org> From: Richard Henderson Message-ID: <170b1d50-72b5-72c1-7bc5-9c41d84425cf@linaro.org> Date: Thu, 30 Jan 2020 08:09:39 -0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 2607:f8b0:4864:20::642 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: david@gibson.dropbear.id.au, qemu-ppc@nongnu.org, QEMU Developers , Howard Spoelstra Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 1/29/20 5:35 PM, Aleksandar Markovic wrote: > 00:51 Čet, 30.01.2020. Richard Henderson > је написао/ла: >> >> The first two address the performance regression noticed >> by Howard Spoelstra.  The last two are just something I >> noticed at the same time. >> > > But, performance regression, according to Howard bisect analysis, happened > because of the change in target-independant code, and the fix presented here is > in target-specific code. This defies basic logic and deserves clear and > detailed explanation. > > My additional concern, of course, is: Are other targets exposed to performance > degradation, and why? Potentially, yes. However: It requires lots of loads in a loop, on a hot path. I would not have guessed that the ppc32 Load Multiple Word (et al) was on a hot path at all, since the instructions are deprecated. But that's what an ancient os gets you, I suppose. r~