[illumos-Developer] initial review: bombproof taskq dispatch

[Gordon Ross]

On Wed, Jul 6, 2011 at 8:06 PM, Garrett D'Amore <garrett at nexenta.com> wrote:
> On Wed, 2011-07-06 at 19:30 -0400, Albert Lee wrote:
>> On Thu, Jun 30, 2011 at 1:36 PM, Albert Lee <trisk at opensolaris.org> wrote:
>> > On Wed, May 4, 2011 at 8:11 PM, Garrett D'Amore <garrett at nexenta.com> wrote:
>> >> On Wed, 2011-05-04 at 18:52 -0500, Jason King wrote:
>> >>
>> >>>
>> >>>
>> >>>
>> >>> With the preface that a number of these questions are also partially
>> >>> for my own edification, so these might be more than a bit ignorant :)
>> >>>
>> >>>
>> >>> This change would seem to ignore any limits on the number of threads
>> >>> for a taskq (or rather it appears you could create more static
>> >>> taskq_ent_t's than the limit for the taskq & dispatch all of them).
>> >>> A lot of the logic within taskq_dispatch seems to depend on this limit
>> >>> (and in fact the taskq itself allocates max_nthreads # of kthread_t
>> >>> structures).  Is this correct?
>> >>
>> >> Nothing I've done touches the threading stuff... the only thing is that
>> >> my stuff is totally incompatible with dynamic taskqs.  Folks using
>> >> dynamic taskqs don't want this prealloc behavior anyway, because dynamic
>> >> taskq dispatch might actually create whole threads. :-)
>> >>
>> >
>> > We have an effectively unlimited queue length here, given that we
>> > ignore taskq_{min,max}alloc. Those values are specified at
>> > taskq_create separately from the thread count, though.
>> >
>> > -Albert
>> >
>>
>> Gordon pointed out in the Nexenta review that flags = TQ_SLEEP should
>> still remain for zio so as not to change the #ifndef _KERNEL
>> behaviour. Sorry to derail your RTI.
>
> TQ_SLEEP vs. DDI_NOSLEEP have no difference for userland.  They both
> just call malloc().  Anyway, those changes were not in this code, but in
> your changes to iscsit, which is not part of this cset.
>
>        - Garrett

Yes, it was not clear in what I reviewed that TQ_SLEEP==0,
so given that, I'm happy with the zio change either way.

Gordon