Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH/RFC v2 0/6] Convert stop_machine to use a workqueue | Date | Thu, 16 Oct 2008 21:38:42 +1100 |
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On Tuesday 14 October 2008 08:50:07 Heiko Carstens wrote: > Version 2: This is version 2 which converts stop_machine to a workqueue > based implementation as suggested by Rusty instead of trying to extend the > current kernel thread approach. > > This patch series would allow to convert s390 to the generic IPI interface. > We can't to that currently since our etr/stp code relies on the old > semantics of smp_call_function that guarantee that the function only > returns after all receiving cpus have acknowledged the IPI. That way it is > known that all other cpus are running in an interrupt handler with > interrupts disabled. This is not true anymore with the generic IPI > infrastructure. > > So one idea was to use stop_machine in order to synchronize all cpus. Rusty > was kind enough to extend it so that it is now possible to run a function > on several cpus, instead of just one. > However we need to be able to do that without allocating any memory. That's > what this patch set is about: it changes the current stop_machine code to > use a workqueue instead of kernel threads to synchronize all cpus. > This has the advantage that all per cpu workqueue threads are already > running when stop_machine gets called and therefore no memory needs to be > allocated. In addition stop_machine cant't fail anymore (free_module() > relies on that). > > A few things that need to be addressed: > - stop_machine gets called from initcalls, so we need to make sure that it > is already initialized and has its workqueue started before that. For > that a pre_smp initcall (early_initcall) is used to initialize it. > - the stop_machine kernel threads used to be rt kernel threads. Workqueues > are normal threads. To get high priority threads a new interface > create_rt_workqueue is introduced. > > Patch 1 Moves the call to init_workqueue before pre smp initcalls > Patch 2 introduces create_rt_workqueue > Patch 3 converts stop_machine to use an rt workqueue
OK, I've taken 1-3. Hope for Ingo's ack on 1 and 2. I'm holding out on 4, and hopefully s390 can merge after this is done.
Thanks! Rusty.
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