Messages in this thread | | | Date | Wed, 19 Aug 2009 21:41:19 +0530 | From | "K.Prasad" <> | Subject | Re: [Patch 0/1] HW-BKPT: Allow per-cpu kernel-space Hardware Breakpoint requests |
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On Mon, Aug 17, 2009 at 06:16:41PM +0530, K.Prasad wrote: > Hi All, > Please find a patch that enables kernel-space breakpoints to be > requested for a subset of the available CPUs in the system. This allows > per-CPU breakpoints and comes with the associated benefit of reduced > overhead during (un)registration. > > This enhancement allows exploitation of hardware breakpoint registers by > 'perf' which produces a CPU-wise information. > > Design changes > -------------- > - Every breakpoint request 'consumes' the first available debug register > (starting from HBP_NUM) in each CPU represented by 'cpumask' field in > 'struct hw_breakpoint'. > > - 'hbp_kernel_pos' (that separates kernel-space breakpoints from the > free/user-space breakpoints) now points to the maximum of debug > registers consumed on any given CPU. > -- 'hbp_kernel_pos' is decremented (one-at-a-time) to allow a new-slot > for kernel-space requests iff all debug registers on the given CPU > (from HBP_NUM - 1 to 'hbp_kernel_pos' are already consumed. > -- 'hbp_kernel_pos' is incremented (one-at-a-time) to free a slot iff > a removal request results in the release of a bkpt request that > consumed maximum debug registers for kernel-space. > > - Every removal request results in compaction of breakpoint registers > (on a per-cpu basis) to occupy the vacant debug register. > > The patch is based on commit b6c720b811aed0eeda89f277f13c1bd1bdf721fd of > -tip tree and has been tested to work fine on an x86 machine for both > cases (i.e. system-wide kernel breakpoints and bkpts for a subset of CPUs). > > Please let me know your comments on the same. > > Thanks, > K.Prasad >
Hi Frederic, Do you find these patches, that provide the ability to restrict kernel-space breakpoints to any given subset of CPUs, to bring the requisite features for exploitation of hw-bkpt by 'perf tools'?
Also of interest would be the reduced overhead associated with (un)register_kernel_hw_breakpoint() operations (no IPI in case of single-CPU breakpoint request).
Thanks, K.Prasad
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