Nick Piggin wrote: > On Tuesday 26 August 2008 06:15, Gregory Haskins wrote: > >> git-id c4acb2c0669c5c5c9b28e9d02a34b5c67edf7092 attempted to limit >> newidle critical section length by stopping after at least one task >> was moved. Further investigation has shown that there are other >> paths nested further inside the algorithm which still remain that allow >> long latencies to occur with newidle balancing. This patch applies >> the same technique inside balance_tasks() to limit the duration of >> this optional balancing operation. >> >> Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx> >> CC: Nick Piggin <npiggin@xxxxxxx> >> > > Hmm, this (andc4acb2c0669c5c5c9b28e9d02a34b5c67edf7092) still could > increase the amount of work to do significantly for workloads where > the CPU is going idle and pulling tasks over frequently. I don't > really like either of them too much. > I had a feeling you may object to this patch based on your comments on the first one. Thats why I CC'd you so you wouldnt think I was trying to sneak something past ;) > Maybe increasing the limit would effectively amortize most of the > problem (say, limit to move 16 tasks at most). > The problem I was seeing was that even moving 2 was too many in the ftraces traces I looked at. I think the idea of making a variable limit (set via a sysctl, etc) here is a good one, but I would recommend we have the default be "1" for CONFIG_PREEMPT (or at least CONFIG_PREEMPT_RT) based on what I know right now. I know last time you objected to any kind of special cases for the preemptible kernels, but I think this is a good compromise. Would this be acceptable? Thanks Nick, -Greg
Attachment:
signature.asc
Description: OpenPGP digital signature
