On Mon, Dec 30, 2013 at 4:12 PM, Ben Pfaff <b...@nicira.com> wrote:
> On Mon, Dec 30, 2013 at 03:56:38PM -0800, Pravin Shelar wrote:
>> On Mon, Dec 30, 2013 at 3:32 PM, Ben Pfaff <b...@nicira.com> wrote:
>> > On Mon, Dec 30, 2013 at 03:05:56PM -0800, Pravin Shelar wrote:
>> >> On Mon, Dec 30, 2013 at 2:44 PM, Ben Pfaff <b...@nicira.com> wrote:
>> >> > On Mon, Dec 30, 2013 at 02:37:38PM -0800, Pravin Shelar wrote:
>> >> >> On Mon, Dec 30, 2013 at 1:34 PM, Ben Pfaff <b...@nicira.com> wrote:
>> >> >> > On Mon, Dec 30, 2013 at 11:10:22AM -0800, Pravin Shelar wrote:
>> >> >> >> On Mon, Dec 30, 2013 at 10:49 AM, Ben Pfaff <b...@nicira.com> wrote:
>> >> >> >> > On Mon, Dec 30, 2013 at 10:40:13AM -0800, Pravin Shelar wrote:
>> >> >> >> >> On Fri, Dec 27, 2013 at 8:03 PM, Ben Pfaff <b...@nicira.com>
>> >> >> >> >> wrote:
>> >> >> >> >> > ovsthread_counter is an abstract interface that could be
>> >> >> >> >> > implemented
>> >> >> >> >> > different ways. The initial implementation is simple but less
>> >> >> >> >> > than
>> >> >> >> >> > optimally efficient.
>> >> >> >> >> >
>> >> >> >> >> > Signed-off-by: Ben Pfaff <b...@nicira.com>
>> >> >> >> >> > +void
>> >> >> >> >> > +ovsthread_counter_inc(struct ovsthread_counter *c, unsigned
>> >> >> >> >> > long long int n)
>> >> >> >> >> > +{
>> >> >> >> >> > + c = &c[hash_int(ovsthread_id_self(), 0) % N_COUNTERS];
>> >> >> >> >> > +
>> >> >> >> >> Does it make sense optimize this locking so that threads running
>> >> >> >> >> on
>> >> >> >> >> same numa-node likely share lock?
>> >> >> >> >> we can use process id hashing to achieve it easily.
>> >> >> >> >
>> >> >> >> > Yes, that makes a lot of sense. How do we do it?
>> >> >> >> >
>> >> >> >> Use processor id (sched_getcpu()) to hash it. In case of
>> >> >> >> sched_getcpu() is not available then we can read thread affinity
>> >> >> >> using
>> >> >> >> sched_getaffinity() and return assigned CPU, in properly optimized
>> >> >> >> environment we can assume that a thread wold be pinned to one cpu
>> >> >> >> only. But I am not sure of doing on platforms other than linux.
>> >> >> >
>> >> >> > That's reasonable.
>> >> >> >
>> >> >> > But, on second thought, I am not sure of the benefit from threads on
>> >> >> > the same node sharing a lock. I see that there are benefits from
>> >> >> > threads on different nodes having different locks, but I'm not sure
>> >> >> > that using only one lock on a single node really saves anything.
>> >> >> > What
>> >> >> > do you think?
>> >> >>
>> >> >> Then how about having per-cpu lock?
>> >> >
>> >> > That would be ideal but how would I do it?
>> >>
>> >> Create array of ovsthread_counter__ for all possible cpu. So
>> >> N_COUNTERS would be variable equal to num of possible cpu. To
>> >> increment use counter at index sched_getcpu().
>> >
>> > You make it sound easy ;-) I think that's harder than it sounds. "All
>> > possible cpus" is hard to figure out (is it possible from userspace?)
>> > especially since the number of cpus can increase or decrease. I don't
>> > know of a guarantee that cpus are numbered consecutively from 0 (from
>> > 1?) so we'd probably need a hash table instead of an array. We'd
>> > probably need a mutex anyway because there's no guarantee that
>> > the process doesn't get migrated between cpus while running this
>> > code. And we'd still need a fallback for non-Linux.
>> >
>> Depending on kernel, max cpu id can be calculated by a system call or
>> sysfs read.
>
> For future reference, which syscall or sysfs object is that?
>
sysconf(_SC_NPROCESSORS_CONF): number of possible CPU.
sched_getaffinity(): by examining returned CPU mask.
sysfs: /sys/devices/system/cpu/possible
procfs: /proc/cpuinfo
> I'm leaning toward just putting a mutex around these variables, and
> skipping the ovsthread_counter abstraction entirely for now.
I am fine with optimizing it later.
_______________________________________________
dev mailing list
dev@openvswitch.org
http://openvswitch.org/mailman/listinfo/dev
