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See http://www.infradead.org/rpr.html X-Rspam-User: X-Rspamd-Queue-Id: 063CF20009 X-Rspamd-Server: rspam03 X-Stat-Signature: sj89gbewmjcagn6rs5fxgsnzbmjr8cbj X-HE-Tag: 1761109490-196028 X-HE-Meta: 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 dhp2COOv suRzTBdTBXb8+/8ivJIwa4rPo4EuDgkLw7CXBHRSJFNbA38Lya8Wp2zBpj0ciTmvtNgAg668EXIunnO4mThs8NtaxojftiedunlHpHNliqMeco+TuJ9rZ55DohLiSbgvXyBotI+JwccytPUXXmvx0DGukQMqp1OMQYVAQarpi/jQCBxvwkMVwa5HtOt+eVzm+rUbT/ZUVxoHULjFM/NTTA0uygEnzIpxoC+AZ X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 22, 2025 at 12:57:51PM +1030, Qu Wenruo wrote: > My VM is using kvm64 CPU type, which blocks quite a lot of CPU features, > thus the CRC32 performance is pretty poor. Yes, unaccelerated CRC32 is a bad idea. > > I just tried a short hack to always make direct IO to fallback to buffered > IO, the nodatasum performance is the same as the bouncing page solution, so > the slow down is not page cache itself but really the checksum. > > With CPU features all passed to the VM, the falling-back-to-buffered direct > IO performance is only slightly worse (10~20%) than nodatasum cases. I'm a bit lost, what are the exact cases you are comparing here?