lkml.org 
[lkml]   [2021]   [Sep]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 0/7] proc/stat: Maintain monotonicity of "intr" and "softirq"
    From
    Date
    On Sun, Sep 12, 2021, at 18:30, Alexey Dobriyan wrote:
    > How about making everything "unsigned long" or even "u64" like NIC
    > drivers do?

    I see some possible hurdles ahead:

    - Not all architectures have atomic operations for 64-bit values

    All those "unsigned int" counters are incremented with __this_cpu_inc()
    which tries to use atomics if possible. Though, I'm not quite sure
    how this works for read side which does not seem to use atomic reads
    at all. I guess, just by the virtue of properly aligned 32-bit reads
    being atomic everywhere? If that's so, I think widening counters to
    64 bits will come with an asterisk.

    - We'll need to update all counters to be 64-bit.

    Like, *everyone*. Every field that gets summed up needs to be 64-bit
    (or else wrap-arounds will be incorrect). Basically every counter in
    every irq_cpustat_t will need to become twice as wide. If that's
    a fine price to pay for accurate, full-width counters...

    Previously I thought that some of these counters even come from
    hardware, but now that I'm reviewing them, that does not seem to be
    the case. Thankfully.

    So right now I don't see why it shouldn't be doable in theory.
    I'll give it a shot, I guess, and see how it works in practice,
    at least as far as the patches go (since I can't really test on all
    architectures).

    \
     
     \ /
      Last update: 2021-09-12 14:37    [W:4.245 / U:0.032 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site