Re: [patch v2 0/3] OProfile support for System z's hardware sampling

[Heinz Graalfs <graalfs@linux.vnet.ibm.com>]

Hello Robert,

when do you have a chance do look at my patches?

Looking forward to a positive reply.

Heinz

On Fri, 2011-01-21 at 11:06 +0100, Heinz Graalfs wrote:
> Hello Robert,
> 
> I'm resending yesterday's mail because I missed to specify the correct sender information.
> 
> This is a re-posting of the patch series originally posted last month:
> 
> http://marc.info/?l=linux-s390&m=129285043619973&w=2
> 
> Heinz
> 
> Changes in
> 
> v2:
>    - kernel module hwsampler removed, everything is now in oprofile kernel module
>    - functions from hwsampler-main.c and smpctl.c merged into arch/s390/oprofile/hwsampler.c
>      - functions made static
>    - arch/s390/include/asm/hwsampler.h moved to arch/s390/oprofile/hwsampler.h
>      - structs have now hws_ prefix
>    - config variables changed, HAVE_HWSAMPLER used only
>    - original patch 4 (handle_munmap.patch) removed
> 
> Description:
> 
> So far, OProfile takes samples by using a software interrupt.
> The purpose of this series of patches is to add support for System z hardware sampling to OProfile.
> 
> Hardware (HW) sampling is a feature provided by System z processors (z10 and follow ons).
> When sampling, the processor takes samples containing the instruction address, PID, and other information.
> The samples are taken at a programmable rate and stored into a buffer provided by the operating system.
> The sampling process is implemented in hardware and millicode and thus does not affect the operating system
> being oberved, apart from requiring buffer memory that the Linux kernel must provide.
> 
> Hardware sampling is available in LPAR mode on 64 BIT processors only.
> 
> The overall approach is to replace the software-based sample generation by hardware sampling.
> All required functionality to control the HW sampling mechanism is added to the oprofile kernel module.
> The functions provide support for
>  - controlling the sampling hardware,
>  - setting up appropriate buffer structures (HW buffers),
>  - retrieving sample entries from these buffers.
> Multiple CPUs can be handled.
> 
> The samples contain the instruction address, a bit distinguishing between kernel and user space,
> and for user space samples also the PID.
> Instead of taking samples from its own per-CPU buffers, OProfile would rather take samples from the
> HW buffers.
> 
> When hardware sampling can be enabled on the current System z processor it will be the new default.
> Switching back to timer based sampling can be established by using
> 
>    echo 0 > /dev/oprofile/hwsampling/hwsampler
> 
> The user space drivers of OProfile also need an extension to control hw sampling by appropriate options.
> 
> 
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