lkml.org 
[lkml]   [2012]   [Feb]   [10]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [v7 0/8] Reduce cross CPU IPI interference
    From
    Date
    On Thu, 2012-02-02 at 10:41 -0500, Chris Metcalf wrote:
    >
    > /*
    > * Quiesce the timer interrupt before returning to user space after a
    > * system call. Normally if a task on a dataplane core makes a
    > * syscall, the system will run one or more timer ticks after the
    > * syscall has completed, causing unexpected interrupts in userspace.
    > * Setting DP_QUIESCE avoids that problem by having the kernel "hold"
    > * the task in kernel mode until the timer ticks are complete. This
    > * will make syscalls dramatically slower.
    > *
    > * If multiple dataplane tasks are scheduled on a single core, this
    > * in effect silently disables DP_QUIESCE, which allows the tasks to make
    > * progress, but without actually disabling the timer tick.
    > */
    > #define DP_QUIESCE 0x1

    This is what Frederics work does

    >
    > /*
    > * Disallow the application from entering the kernel in any way,
    > * unless it calls set_dataplane() again without this bit set.
    > * Issuing any other syscall or causing a page fault would generate a
    > * kernel message, and "kill -9" the process.
    > *
    > * Setting this flag automatically sets DP_QUIESCE as well.
    > */
    > #define DP_STRICT 0x2

    This is a debug feature.. you'd better know what your own software does.

    >
    > /*
    > * Debug dataplane interrupts, so that if any interrupt source
    > * attempts to involve a dataplane cpu, a kernel message and stack
    > * backtrace will be generated on the console. As this warning is a
    > * slow event, it may make sense to avoid this mode in production code
    > * to avoid making any possible interrupts even more heavyweight.
    > *
    > * Setting this flag automatically sets DP_QUIESCE as well.
    > */
    > #define DP_DEBUG 0x4

    This too is a debug feature, one that doesn't cover all possible
    scenarios.

    > /*
    > * Cause all memory mappings to be populated in the page table.
    > * Specifying this when entering dataplane mode ensures that no future
    > * page fault events will occur to cause interrupts into the Linux
    > * kernel, as long as no new mappings are installed by mmap(), etc.
    > * Note that since the hardware TLB is of finite size, there will
    > * still be the potential for TLB misses that the hypervisor handles,
    > * either via its software TLB cache (fast path) or by walking the
    > * kernel page tables (slow path), so touching large amounts of memory
    > * will still incur hypervisor interrupt overhead.
    > */
    > #define DP_POPULATE 0x8

    map()s MAP_POPULATE will pre-populate the stuff for you, as will
    mlock(), the latter will (mostly) ensure they stay around.



    \
     
     \ /
      Last update: 2012-02-10 19:41    [W:0.027 / U:0.740 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site