Hi, > On 20/07/2010 18:41, Johnson Earls wrote: > > Hello, > > > > I am hoping that someone on this list can enlighten > me about the DTrace i/o provider. I am apparently > not understanding where the i/o provider actually > sits in the stack. > > > > My understanding, from reading > http://wikis.sun.com/display/DTrace/io+Provider, is > that (discounting NFS for this purpose) the i/o > provider probes fire when I/O is going to a specific > disk device - in other words, below the filesystem > layer. > > > > I am using both the iopattern dtrace script and my > own dtrace script modified from the iopattern script > to gather read and write bandwidth statistics on a > fibre channel SAN disk device. I do this through the > io:genunix::start and io:genunix::done probe, > filtering on args[1]->dev_statname for the disk > device name and accumulating the bandwidth statistics > from args[0]->b_count. > > > > However, I am seeing occasional reports of i/o > bandwidth anywhere from 40 to 100 GB per second, on a > 4Gbps fiber channel device. I am obviously not > understanding how the io provider is working. > > > > My questions: > > > > Do io:genunix::start and io:genunix::done fire > *only* for physical device access, or will they fire > when the request is being served by a Solaris cache? > > > > If they fire on requests that are served by a > cache, is there any way to determine this in order to > filter those results out? > > > > If they fire only on physical device access, what > can explain the buffer counts being reported at many > times higher than what the physical device is capable > of? > > > > > Check documentation for args[0]->b_flags, for > example: > > io:::start > { > printf("%s\n", args[0]->b_flags&B_PHYS ? > "physical":logical"); > > _______________________________________________ > dtrace-discuss mailing list > dtrace-discuss@opensolaris.org > The B_PHYS flag is set for accessing the "raw" device (i.e., /dev/rdsk/...). Access to the block device, regular files, directories will not have B_PHYS set, but still are accessing the disk. The io:genunix:bdev_strategy:start and io:genunix:biodone:done probes fire when the buffer is being handed to the disk driver, and when the I/O has completed. In other words, they are not triggering on cache access but physical device access. As to why you are seeing impossible values, I would have to see your script.
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