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b=KXNW41KLzQ1yC6X9sBVothBySUpd3PSXV4JllhANSOalEfcpiwo6d5L0T8AZr7dEs TrjheJfwildl4CcMFu95Dxp0GqYTZ13gp6N2ZVDI3gKLfI9E5k+mRnp7LfI9xV+B5p F/mFAF80BasobGaeOMy1/9b4HtfluEtl0rqk39aBo5jzS09pu+yLS1ayQOBeXt/gv4 rylHAXIPR9aqK38aeizkcBCVzai9NpqSfrDVP+jbkYEFw8S3xPMEfjA631WONK0gch 7T6/mLPfYzI28GJAexJA4kEdCwj6lE2Uwnre3ov2sLvxjIkLZ2agG4pZgjb+SH21AV pFFl8SDa5I8+Q== From: SeongJae Park To: Josh Law Cc: SeongJae Park , akpm@linux-foundation.org, damon@lists.linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 2/2] mm/damon/core: eliminate hot-path integer division in damon_max_nr_accesses() Date: Mon, 23 Mar 2026 07:10:36 -0700 Message-ID: <20260323141037.80243-1-sj@kernel.org> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260322214325.260007-3-objecting@objecting.org> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: E4D6240014 X-Stat-Signature: ig3xejw46rbbaisbgr1py1sis479zirw X-Rspam-User: X-HE-Tag: 1774275044-467629 X-HE-Meta: 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 z7UkSKMD sT/qhkLNIhP++ADMHOTaZULS2pK0/HVxUw/M6ELBvph6KmDA3aPFLCdXZ8qAeKEOgNZUIFq40t1OiE/x9J5mIQVrhNKv223GU8mHMgKbHYSnha4z9X2RD9G1T4Zkt7LkAJb5jiIVpW9G3ldCvZZtwgEN+SF6CuHfQTT5WwDxQhXDbWP+QaptvolbTs1VU1TgXSGOh8FMID0ufCJWGvAVSS80rb60YCMupMcl6VlKUYTX86r8kaQzS7z+qbl65orYD0eoohdsJc+CLsp4/5npn8AaAteQoye2m27Qn4kPK0JicVQJ9wyD4iGRDyZiP62zyT/inPgxnq4Vrc1ht/kb7rcFzcIiNqgfhRWY4wVgEUb6YicU= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 22 Mar 2026 21:43:25 +0000 Josh Law wrote: > Hardware integer division is slow. The function damon_max_nr_accesses(), > which is called very frequently (e.g., once per region per sample > interval inside damon_update_region_access_rate), performs an integer > division: attrs->aggr_interval / attrs->sample_interval. > > However, the struct damon_attrs already caches this exact ratio in the > internal field aggr_samples (since earlier commits). We can eliminate > the hardware division in the hot path by simply returning aggr_samples. > > This significantly reduces the CPU cycle overhead of updating the access > rates for thousands of regions. > > Signed-off-by: Josh Law Reviewed-by: SeongJae Park Thanks, SJ [...]