----- Original Message -----
>
>
> ----- Original Message -----
> > task_exists() scans known tasks for a given task address.
> >
> > refresh_radix_tree_task_table() looks like:
> > hq_open()
> > for cpus {
> > hq_enter(per_cpu_idle_thread)
> > }
> > for ... {
> > hq_enter(task)
> > }
> > hq_close()
> >
> > tt->running_tasks = 0
> > for task in retrieve_list(hq_entries) {
> > if (task_exists()) {
> > duplicate task address
> > continue
> > }
> > add_context()
> > }
> >
> > Because retrieve_list returns unique tasks, the above task_exists()
> > check will never find a duplicate task. So remove the check. This
> > converts the above loop from O(N^2) to O(N) which saves considerable
> > startup time when there are a large number of tasks. On a 1M task dump
> > this patch reduces startup time: 44m => 1m.
> >
> > I was not able to test the other pid table routines, but I suspect they
> > may also benefit from similar removal.
>
> Hi Greg,
>
> I'm thinking that the task_exists() removal may be the most beneficial
> piece of the patch set, right?
>
> I have a set of ~250 vmcore files gathered over the years, but only 2 of
> them are from kernels using the idr radix tree scheme. I timed how long
> it took to simply bring up all 250 vmcores to their crash prompt and then
> quit immediately. These are the total times running with and without your
> patch:
>
> without the patch:
>
> real 46m44.023s
> user 17m29.956s
> sys 0m58.940s
>
> with your patch applied:
>
> real 46m39.752s
> user 17m36.496s
> sys 0m58.269s
>
> But as you've noted, given that all of the various refresh_xxx functions
> use hq_enter(), the task_exists() call is pretty much useless.
>
> I'm going to remove the task_exists() call from the remaining refresh_xxx
> functions, rerun the test, and see how it affects the numbers. I suspect
> it will help a bit, although the task count in the ~250 vmcores range from
> 22 to 4178, with only ~20 dumpfiles having more than 1000 tasks.
>
> Thanks,
> Dave
As it turns out, there wasn't any noticeable benefit with my set of dumpfiles:
without the patch:
real 46m58.872s
user 17m43.273s
sys 1m0.144s
with your patch plus all task_exists() calls removed:
real 46m58.617s
user 17m50.023s
sys 0m58.708s
But obviously the extremely large task count in your dumpfile shows the
benefit. In addition to the task_exists() removals, I also need to update
dump_task_table() to add a display of the context_by_task array (for help -T),
and the INDEXED_CONTEXTS flag (for help -[tT]). When I get it checked in to
github, I'll post the link here as confirmation.
Thanks,
Dave
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