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SubjectRe: question wrt context switching during disk i/o
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)

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