On 2024-07-01 01:06:32+0000, lin jia wrote: > dear sir : > thanks for reply, Mr Thomas, I read the commit log of "sysctl: Stop > requiring explicit management of sysctl directories" , found the > following section of benchmark in sysctl: Stop requiring explicit > management of sysctl directories - kernel/git/sysctl/sysctl.git - > joel.granados's fork of > linux.git<https://git.kernel.org/pub/scm/linux/kernel/git/sysctl/sysctl.git/commit/?id=7ec66d06362da7684a4948c4c2bf1f8546425df4> Please don't top-post, use inline quotes. > > Benchmark before: > make-dummies 0 999 -> 0.7s > rmmod dummy -> 0.07s > make-dummies 0 9999 -> 1m10s > rmmod dummy -> 0.4s > > Benchmark after: > make-dummies 0 999 -> 0.44s > rmmod dummy -> 0.065s > make-dummies 0 9999 -> 1m36s > rmmod dummy -> 0.4s > > does it means the difference on the performance between new implement > and old of sysctl? If that's the case, it seems the difference is not > significant In your original mail you reported that it helps to exit earlier from the loop. This commit completely removes the loop, so I would guess that should be even better. The benchmark probably also depends on the actual usage, did you test yours? Personally I don't know much about the sysctl internals, especially that old ones. So can't give any other advice. > ________________________________ > 发件人: Thomas Weißschuh <thomas@xxxxxxxx> > 发送时间: 2024年6月29日 19:19 > 收件人: lin jia <chinasjtu@xxxxxxx> > 抄送: linux-kernel@xxxxxxxxxxxxxxx <linux-kernel@xxxxxxxxxxxxxxx>; Luis Chamberlain <mcgrof@xxxxxxxxxx>; Kees Cook <keescook@xxxxxxxxxxxx>; Joel Granados <j.granados@xxxxxxxxxxx>; linux-fsdevel@xxxxxxxxxxxxxxx <linux-fsdevel@xxxxxxxxxxxxxxx> > 主题: Re: can anyone explain the meaning of improvement of try_attach function in sysctl.c? > > Hi lin jia, > > thanks for posting to the list. > I'll also add Joel, Kees, Luis and the fsdevel lists to Cc, as per > "PROC SYSCTL" from the MAINTAINERS file. > > On 2024-06-29 10:54:15+0000, lin jia wrote: > > Hi all: > > I've been reading the sysctl part of the Linux kernel source code( 3.3.8) recently and encountered some issues. I'm not sure who I can ask for help. > > In sysctl.c , the function of __register_sysctl_paths is to register a sysctl hierarchy, I am confused by the function " try_attach", > > This is a very old kernel. > > The function you mention was removed over ten years ago and the way > sysctls are registered today is completely different. > > > /* see if attaching q to p would be an improvement */ > > static void try_attach(struct ctl_table_header *p, struct ctl_table_header *q) > > > > what is the meaning of "improvement", I don’t know the matching standard for the entry in the list > > > > another question is , why not break when variable is_better and > > not_in_parent is true, so as to save time, when I config about 2k~4k > > net device objects in system, "register_net_sysctl_table" cost > > considerable time. > > try_attach() was removed in > commit 7ec66d06362d ("sysctl: Stop requiring explicit management of sysctl directories") > citing performance reasons. > This may be same performance issue you are encountering and maybe you > can take inspiration from that commit to avoid it. > > Or even better, upgrade to a newer kernel. > > > <snip> > > > Thomas
