Hi! On 11:40 Tue 15 Nov , Kai Meyer wrote: > On 11/15/2011 11:13 AM, michi1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx wrote: ... > > You might want to take a look at wait queues (the kernel equivalent to pthread > > "condidions"). Basically you instead of calling msleep(), you call > > wait_event(). In the function which decrements numbios, you check whether it > > is 0 and if so call wake_up(). ... > That sounds very promising. When I read up on wait_event here: > lxr.linux.no/#linux+v2.6.32/include/linux/wait.h#L191 > > It sounds like it's basically doing the same thing. I would call it like so: > > wait_event(wq, atomic_read(numbios) == 0); Yes, you dol something like this. > To make sure I understand, this seems very much like what I'm doing, > except I'm being woken up every time a bio finishes instead of being > woken up once every millisecond. That is, I'm assuming I would use the > same work queue for all my bios. You are *not* woken up every time you a bio finishes. You are woken up every time you call wake_up(). You could do something like: if (atomic_dec_return(numbios) == 0) wake_up(wp); > During my testing, when I do a lot of disk I/O, I may potentially have > hundreds of threads waiting on anywhere between 1 and 32 bios. Help me > understand the sort of impact you think I might see between having > hundreds waiting for a millisecond, and having hundreds get woken up > each time a bio completes. It seems like it would be very helpful in low > I/O scenarios, especially when there are fast disks involved. I'm > concerned that during heavy I/O loads, I'll be doing a lot of > atomic_reads, and I have the impression that atomic_read isn't the > cheapest operation. The wakeups might some some overhead. However, I would worry more about scheduling overhead on smp systems than atomic_read performance. -Michi -- programing a layer 3+4 network protocol for mesh networks see http://michaelblizek.twilightparadox.com _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
