Messages in this thread | | | Date | Wed, 25 Oct 2006 00:27:52 +0200 | From | Martin Peschke <> | Subject | Re: [Patch 0/5] I/O statistics through request queues |
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Phillip Susi wrote: > This discussion seems to involve two different solutions to two > different problems. If it is a simple counter you want to be able to > poll, then sysfs/debugfs is an appropriate place to make the count > available. If it is a detailed log of IO requests that you are after, > then blktrace is appropriate.
It's about counters ... well, sometimes a buch of counters called histogram.
> I did not read the patch to see, so I must ask: does it merely keep > statistics or does it log events? If it is just statistics you are > after, then clearly blktrace is not the appropriate tool to use.
If matters were as simple as that, sigh.
Statistics feed on data reported through events. "Oh, this request has completed - time to update I/O counters."
The tricky question is: is event processing, that is, statistics data aggregation, better done later (in user space), or immediately (in the kernel). Both approaches exist: blktrace/btt vs. gendisk statistics used by iostat, for example.
My feeling was that the in-kernel counters approach of my patch was fine with regard to the purpose of these statistics. But blktrace exists, undeniably, and deserves a closer look.
Martin
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