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Message-ID: <CACRpkdaCyiriM3xLJQ=OmcVRV6YY94mqsyaje1g2Fo_FMC1W6w@mail.gmail.com> Date: Wed, 20 Dec 2017 10:32:51 +0100 From: Linus Walleij <linus.walleij@...aro.org> To: Christophe Leroy <christophe.leroy@....fr> Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, linux-gpio@...r.kernel.org Subject: Re: [PATCH 1/4] gpio: sysfs: change 'value' attribute to prealloc On Mon, Dec 18, 2017 at 11:08 AM, Christophe Leroy <christophe.leroy@....fr> wrote: > The GPIO 'value' attribute is time critical. A small bench with > 'perf record' on the app below shows that 80% of the time spent in > sysfs_kf_seq_show() is spent in memset() for zeroising the buffer. > > |--67.48%--sysfs_kf_seq_show > | | > | |--54.40%--memset > | | > | |--11.49%--dev_attr_show > | | | > | | |--10.06%--value_show > | | | | > | | | |--4.75%--sprintf > | | | | | > > This patch changes the attribute type to prealloc, eliminating the > need to zeroise the buffer at each read. 'perf record' gives the > following result. > > |--42.41%--sysfs_kf_read > | | > | |--39.73%--dev_attr_show > | | | > | | |--38.23%--value_show > | | | | > | | | |--29.22%--sprintf > | | | | | > > Test done with the following small app: > > int main(int argc, char **argv) > { > int fd = open(argv[1], O_RDONLY); > > for (;;) { > int buf[512]; > > read(fd, buf, 512); > lseek(fd, 0, SEEK_SET); > } > exit(0); > } > > Signed-off-by: Christophe Leroy <christophe.leroy@....fr> I applied this because I don't want to waste honest development efforts. Fixes and improvements I can accept. But not extensions. But as Bartosz says it would be nice to focus efforts on the non-deprecated ABI. Yours, Linus Walleij
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