When modifying netclassid, the command("echo 0x100001 > net_cls.classid")
will take more time on many threads of one process, because the process
create many fds.
for example, one process exists 28000 fds and 60000 threads, echo command
will task 45 seconds.
Now, we only consider the main process when exec "iterate_fd", and the
time is about 52 milliseconds.

Signed-off-by: Liansen Zhai <zhailiansen@kuaishou.com>
---
 net/core/netclassid_cgroup.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/net/core/netclassid_cgroup.c b/net/core/netclassid_cgroup.c
index d6a70ae..d22f091 100644
--- a/net/core/netclassid_cgroup.c
+++ b/net/core/netclassid_cgroup.c
@@ -88,6 +88,12 @@ static void update_classid_task(struct task_struct *p, u32 classid)
 	};
 	unsigned int fd = 0;
 
+	/* Only update the leader task, when many threads in this task,
+	 * so it can avoid the useless traversal.
+	 */
+	if (p != p->group_leader)
+		return;
+
 	do {
 		task_lock(p);
 		fd = iterate_fd(p->files, fd, update_classid_sock, &ctx);
-- 
1.8.3.1

Hello:

This patch was applied to netdev/net-next.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Thu, 12 Oct 2023 17:03:30 +0800 you wrote:
> When modifying netclassid, the command("echo 0x100001 > net_cls.classid")
> will take more time on many threads of one process, because the process
> create many fds.
> for example, one process exists 28000 fds and 60000 threads, echo command
> will task 45 seconds.
> Now, we only consider the main process when exec "iterate_fd", and the
> time is about 52 milliseconds.
> 
> [...]

Here is the summary with links:
  - [net-next,v2] cgroup, netclassid: on modifying netclassid in cgroup, only consider the main process.
    https://git.kernel.org/netdev/net-next/c/c60991f8e187

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

On Thu, Oct 12, 2023 at 05:03:30PM +0800, Liansen Zhai wrote:
> When modifying netclassid, the command("echo 0x100001 > net_cls.classid")
> will take more time on many threads of one process, because the process
> create many fds.
> for example, one process exists 28000 fds and 60000 threads, echo command
> will task 45 seconds.
> Now, we only consider the main process when exec "iterate_fd", and the
> time is about 52 milliseconds.
> 
> Signed-off-by: Liansen Zhai <zhailiansen@kuaishou.com>

Thanks for addressing my review of v1.

Reviewed-by: Simon Horman <horms@kernel.org>