On Thu, Feb 28, 2008 at 08:51:12AM -0800, Gordon Marler wrote:
> The Release notes for Veritas Storage Foundation state that the reason you
> cannot do fbt tracing of their vxio driver is because it's text size is
> larger than 2 MB:
>
> Dynamic Tracing Function Boundary Tracing probes
> Dynamic Tracing (DTrace) Function Boundary Tracing (FBT) probes are not
> supported with the vxio driver. This is because of a limitation in Solaris 10
> that
> such probes cannot handle modules with a text size larger than 2MB. The
> following error message is generated on the console as a result of using
> DTrace
> FBT probes with the vxio driver:
> fbt: WARNING: couldn?t allocate FBT table for module vxio
> These messages are harmless, and can be safely ignored.
>
> Here's the size we come up with for the module:
>
> # /usr/ccs/bin/size -f /kernel/drv/sparcv9/vxio
> 2915048(.text) + 64696(.rodata) + 241920(.rodata1) + 99120(.data) +
> 79624(.data1) + 6728(.bss) = 3407136
>
> Is there a fix or workaround in the works for this? We're looking to use
> vxio fbt probes but obviously can't until this is resolved. Asking Symantec
> to lower the size of their text area is a non-starter.
It's only an issue on SPARC, not on x86. And there is very little chance
that modules greater than 2MB are going to be instrumentable by DTrace:
the limitation is a limitation in the instruction set architecture (branch
displacements are a signed 4MB quantity). When one is talking about
modules that are greater than 2MB on SPARC, one is essentially talking only
about vxio -- and I think it's safe to say that Sun is not about to bear
an inordinate cost simply to be able to instrument a module that we feel
is obviated by ZFS. ;)
And should Symantec wish to sponsor the work, we would encourage them to
instead break up their absurdly large module. (Note that this module
is larger than the kernel itself -- there's really no excuse for that
much kernel text.)
Not that I have any opinions on this, of course... ;)
- Bryan
--------------------------------------------------------------------------
Bryan Cantrill, Sun Microsystems Fishworks. http://blogs.sun.com/bmc
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