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Mon, 24 Mar 2025 07:25:37 -0700 (PDT) Message-ID: <3ea4b352-c679-45e8-8ab9-84ba074c3e88@tuxon.dev> Date: Mon, 24 Mar 2025 16:25:35 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH] mm: page_alloc: Add kernel parameter to select maximum PCP batch scale number To: corbet@lwn.net, akpm@linux-foundation.org, thuth@redhat.com, rostedt@goodmis.org, paulmck@kernel.org, xiongwei.song@windriver.com, ying.huang@intel.com Cc: linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, geert+renesas@glider.be, wsa+renesas@sang-engineering.com, Claudiu Beznea References: <20241126095138.1832464-1-claudiu.beznea.uj@bp.renesas.com> From: Claudiu Beznea Content-Language: en-US In-Reply-To: <20241126095138.1832464-1-claudiu.beznea.uj@bp.renesas.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi, On 26.11.2024 11:51, Claudiu wrote: > From: Claudiu Beznea > > Commit 52166607ecc9 ("mm: restrict the pcp batch scale factor to avoid > too long latency") introduced default PCP (Per-CPU Pageset) batch size as > a configuration flag. The configuration flag is CONFIG_PCP_BATCH_SCALE_MAX. > > The ARM64 defconfig has CONFIG_PCP_BATCH_SCALE_MAX=5. This defconfig > is used by a high range of SoCs. > > The Renesas RZ/G3S SoC is a single CPU SoC, with L1$ (I-cache 32Kbytes, > D-cache 32 Kbytes), L3$ (256 Kbytes), but no L2$. It is currently used in > a configuration with 1 GiB RAM size. In this configuration, starting with > commit 52166607ecc9 ("mm: restrict the pcp batch scale factor to avoid too > long latency") the "bonnie++ -d /mnt -u root" benchmark takes ~14 minutes > while previously it took ~10 minutes. The /mnt directory is mounted on SD > card. Same behavior is reproduced on similar Renesas single core devices > (e.g., Renesas RZ/G2UL). > > Add a new kernel parameter to allow systems like Renesas RZ/G3S to > continue have the same performance numbers with the default mainline > ARM64 config. With pcp_batch_scale_max=5 (the default value) the bonnie++ > benchmark takes ~14 minutes while with pcp_batch_scale_max=0 it takes > ~10 minutes. > > Signed-off-by: Claudiu Beznea > --- Can you please let me know your input on this patch? Thank you, Claudiu