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    SubjectRe: [PATCH 03/22] 2.6.22-rc3 perfmon2 : new system calls support
    On Tue, May 29, 2007 at 06:48:17AM -0700, Stephane Eranian wrote:
    > sys_pfm_create_context():
    > - create a new perfmon2 context and returns a file descriptor in
    > the pfarg_ctx_t parameters. This is the first call an application
    > must make to do monitoring
    > - rewritten to pass sampling format identification as a string
    > - file descriptor is now returned by call
    >
    > sys_pfm_write_pmcs():
    > - program the PMU configuration registers. Accepts vector of arguments
    > of type pfarg_pmc_t
    >
    > sys_pfm_write_pmds():
    > - program the PMU data registers. Accepts a vector of arguments of type
    > pfarg_pmd_t
    >
    > sys_pfm_read_pmds():
    > - read the PMU data registers. Accepts a vector of arguments of type
    > pfarg_pmd_t

    This kind of interface doesn't make any sense at all. Information should
    be read and written from filedescriptors using the read and write family
    syscalls and through the VFS instead of adding tons of system calls.

    I fear we need to write down the requirements first and then come up
    with something better. E.g. for per-task sampling an interface centered
    around a few files in /proc/<pid>/ would fit very nicely:

    /proc/<pid>/perfmon_pmcs
    /proc/<pid>/perfmon_pmds
    Obvious
    /proc/<pid>/perfmon_ctl
    Can get control commands as ascii sets written to


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