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. -- Michael "Tired" Riepe <michael.riepe@xxxxxxxxxxxxxx> X-Tired: Each morning I get up I die a little -- 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
