Re: building async-calls

On Mon, Dec 17, 2007, Tsantilas Christos wrote:
> Hi Adrian,
> As I am seeing squid3 spends time in EventScheduler::schedule method.
> This method did not affected by the new AsyncCall code. Also this method
> is similar with squid 2.6 eventAdd function.

Yes, but you're using an event system which wasn't designed for massive
amounts of immediate events for, well, massive amounts of immediate events.

> The only I can say is that possibly we are scheduling a huge number of
> events in squid3.

> If the time spend while creating the ev_entry class possibly we need a
> (better?) memory allocator.

.. or don't allocate so many of them.

> Also there is a for loop in this method. Most event scheduled with when=0
> so they attached at the end (or near the end) of the events list (but we
> are running all the list). If we have a big number of events (1000 or
> more) it is possible to spend a lot of time here.
> But if this is the problem it is easy for someone to fix it, we must not
> worry about it at this time....

As the guy who found the bung garbage collection in Squid-3 at least 12 months
ago, causing CPU to chewed through at a crazy rate, I think its worth keeping
this in mind and thinking (and benchmarking!) a way around this.

It shouldn't be that difficult. But what I don't want to see is someone
building an interface which will perform badly, do a whole lot of work
within it, commit sweeping changes to how things are done,
and then wonder why stuff performs badly.

I'm sure its something like:

    for (E = &tasks; *E; E = &(*E)->next) {
        if ((*E)->when > event->when)
            break;
    }

And > should be >=, so it doesn't walk a whole lot of 0.00 (now) events
waiting for them to complete.

Of course, what you guys -should- be doing really is not using this
loop, but instead building a simple dlink list (or whatever data type
in C++ is comparable) and just appending events to the end. O(1) and
all that. This event loop is for scheduling events at some point
in the future and I think overloading it is a bit silly.

Adrian
Received on Mon Dec 17 2007 - 03:14:33 MST