Messages in this thread | | | Date | Thu, 25 Apr 2013 22:59:05 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH documentation 2/2] kthread: Document ways of reducing OS jitter due to per-CPU kthreads |
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On Thu, 25 Apr 2013, Paul E. McKenney wrote: > On Thu, Apr 25, 2013 at 12:23:12PM +0200, Borislav Petkov wrote: > > On Mon, Apr 22, 2013 at 09:03:29PM -0700, Paul E. McKenney wrote: > > > > > +Name: ehca_comp/%u > > > > > +Purpose: Periodically process Infiniband-related work. > > > > > +To reduce corresponding OS jitter, do any of the following: > > > > > +1. Don't use EHCA Infiniband hardware. This will prevent these > > > > > > > > Sounds like this particular hardware is slow and its IRQ handler/softirq > > > > needs a lot of time. Yes, no? > > > > > > > > Can we have a reason why people shouldn't use that hw. > > > > > > Because it has per-CPU kthreads that can cause OS jitter. ;-) > > > > Yeah, I stumbled over this specific brand of Infiniband hw. It looks > > like this particular Infiniband driver uses per-CPU kthreads and the > > others in drivers/infiniband/hw/ don't? > > > > I hope this explains my head-scratching moment here... > > Ah! I rewrote the first sentence to read: > > Don't use eHCA Infiniband hardware, instead choosing hardware > that does not require per-CPU kthreads.
Another option would be to teach that eHCA driver to be configurable on which cpus kthreads are desired and on which not. I can't see a reason (aside of throughput) why that hardware can't cope with a single thread.
Thanks,
tglx
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