* Michael Riepe <michael.riepe@xxxxxxxxxxxxxx> wrote: > Disclaimer: I'm not using UML, but these problems may be related. > > > Bug-Entry : http://bugzilla.kernel.org/show_bug.cgi?id=12208 > > Subject : uml is very slow on 2.6.28 host > > Submitter : Miklos Szeredi <miklos@xxxxxxxxxx> > > Date : 2008-12-12 9:35 (93 days old) > > References : http://marc.info/?l=linux-kernel&m=122907463518593&w=4 > > The other day I noticed a dramatic ptrace slowdown between 2.6.27 and > 2.6.28.x (verified with 2.6.28.8). In particular, a command like > > dd if=/dev/zero of=/dev/null bs=1024k count=1024 > > will normally report a throughput in the GB/s range. On 2.6.27, this is > also true if you run > > strace -o /dev/null <dd command as above> > > which is only a little slower. But if I do the same on 2.6.28.x, I > get a throughput of about 100 MB/s or less, i.e. less than 10%. I > tried the commands on three different machines (an Athlon64 3000+, > a Core Duo T2400 and an Atom 330), and they all behave similar. > The more system calls a program uses, the worse the slowdown (try > the dd command with bs=16k and count=65536, for example - but > don't hold your breath). > > Interestingly, the CPUs are mostly idle while the command is > executing on 2.6.28.x, but there is a high (system) load on > 2.6.27. Therefore, I suspect that it's a scheduling or maybe timer > problem that was introduced between 2.6.27 and 2.6.28. I haven't > had the time to check the rc kernels yet; perhaps someone else can > run a quick check to verify that it's gone in the latest > 2.6.29-rc. that's almost certainly due to the wait_task_inactive() change. Does the patch below improve things? Ingo diff --git a/kernel/sched.c b/kernel/sched.c index 3e827b8..2d60f23 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -2119,7 +2119,8 @@ unsigned long wait_task_inactive(struct task_struct *p, long match_state) * yield - it could be a while. */ if (unlikely(on_rq)) { - schedule_timeout_uninterruptible(1); + cpu_relax(); + cond_resched(); continue; } -- To unsubscribe from this list: send the line "unsubscribe kernel-testers" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
