On Mon, Apr 5, 2021 at 6:08 PM Song Liu [off-list ref] wrote:

quoted

On Apr 5, 2021, at 4:49 PM, Cong Wang [off-list ref] wrote:

On Fri, Apr 2, 2021 at 4:31 PM Song Liu [off-list ref] wrote:

quoted

quoted

On Apr 2, 2021, at 1:57 PM, Cong Wang [off-list ref] wrote:

Ideally I even prefer to create timers in kernel-space too, but as I already
explained, this seems impossible to me.

Would hrtimer (include/linux/hrtimer.h) work?

By impossible, I meant it is impossible (to me) to take a refcnt to the callback
prog if we create the timer in kernel-space. So, hrtimer is the same in this
perspective.

Thanks.

I guess I am not following 100%. Here is what I would propose:

We only introduce a new program type BPF_PROG_TYPE_TIMER. No new map type.
The new program will trigger based on a timer, and the program can somehow
control the period of the timer (for example, via return value).

Like we already discussed, with this approach the "timer" itself is not
visible to kernel, that is, only manageable in user-space. Or do you disagree?

With this approach, the user simply can create multiple timer programs and
hold the fd for them. And these programs trigger up to timer expiration.

Sure, this is precisely why I moved timer creation to user-space to solve
the refcnt issue. ;)

Does this make sense?

Yes, except kernel-space code can't see it. If you look at the timeout map
I had, you will see something like this:

val = lookup(map, key);
if (val && val->expires < now)
   rearm_timer(&timer); // the timer periodically scans the hashmap

For conntrack, this is obviously in kernel-space. The point of the code is to
flush all expired items as soon as possible without doing explicit deletions
which are obviously expensive for the fast path.

Thanks.