Messages in this thread |  | | Date | Sat, 21 Oct 2000 10:24:31 +0200 (CEST) | From | Mike Galbraith <> | Subject | Re: question wrt context switching during disk i/o |
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On Sat, 21 Oct 2000, Mike Galbraith wrote:
> On Fri, 20 Oct 2000, Mark Hahn wrote: > > > > This is something that has been bugging me for a while. I notice > > > on my system that during disk write we do much context switching, > > > but not during disk read. Why is that? > > > > bdflush is broken in current kernels. I posted to linux-mm about this, > > but Rik et al haven't shown any interest. I normally see bursts of > > up to around 40K cs/second when doing writes; I hacked a little > > premption counter into the kernel and verified that they're practially > > all bdflush... > > P.S. > > I took a ktrace snapshot of iozone doing 8k writes. This seems like > a strange and expensive way to only unplug a device ;-) Anyone know > why? > > c010a976 system_call +<22/40> (0.16) pid(257) > c0131bc0 sys_write +<10/d8> (0.12) pid(257) > ... > c010a99a ret_from_sys_call +<6/19> (0.20) pid(257) > c0117f7b schedule +<13/404> (2.14) pid(257->5) > c01091a3 __switch_to +<13/cc> (1.16) pid(5) > c01888c6 generic_unplug_device +<e/38> (0.27) pid(5) > c0117f7b schedule +<13/404> (0.51) pid(5->257) > c01091a3 __switch_to +<13/cc> (0.30) pid(257) > c010a99a ret_from_sys_call +<6/19> (1.20) pid(257)
(arg!) P.P.S
That was perhaps too brief to be clear exactly what I mean.
In a trace segment 263 milliseconds long we switch to kflushd 279 times. 251 of 279 cases are exactly the above.
-Mike
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