lkml.org 
[lkml]   [2007]   [Oct]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    Subjectcoding for optimizations (Re: [PATCH 1/2] i386: mce cleanup part1: functional change)
    From
    On Tue, Oct 09, 2007 at 06:06:05PM +0200, Joerg Roedel wrote:
    > > > void mcheck_init(struct cpuinfo_x86 *c)
    > > > {
    > > > + uint32_t mca, mce;
    > > > +
    > > > if (mce_disabled==1)
    > > > return;
    > > >
    > > > + mca = cpu_has(c, X86_FEATURE_MCA);
    > > > + mce = cpu_has(c, X86_FEATURE_MCE);
    > > > +
    > > > + if (!mca || !mce) {
    > > > + printk(KERN_INFO "CPU%i: No machine check support available\n",
    > > > + smp_processor_id());
    > > > + return;
    > > > + }
    > > > +
    > >
    > > cpu_has() returns int,
    > > but would it be better to have something like
    > >
    > > if (!mce_disabled &&
    > > !(c->x86_capability & (X86_FEATURE_MCA | X86_FEATURE_MCE)) {
    > > printk(KERN_INFO "CPU%i: No machine check support available\n",
    > > smp_processor_id());
    >
    > This looks complicated and is harder to read. Its exactly the purpose of the
    > cpu_has() macro to avoid such constructs.
    >
    > > return;
    > > } else
    > > return;
    >
    > Return unconditionaly here?

    Kind of typo.

    Due to arch code, i think, it must be coded in non-gcc optimistic way. As
    practice and Linus shows, gcc's optimizations sometimes produce very
    unexpected results. People do spaghetti-like coding, without thinking
    about text size / run time.

    Compile time payment was noted by Andrew many years ago:

    "As you know, I'd be more concerned about moves to drop support for the
    older and much faster gcc versions. If you're not using egcs-1.1.2,
    you're already a very patient person." <http://lkml.org/lkml/2001/12/29/163>

    So, i actually wanted to write this:

    if (!mce_disabled) {
    if (!(c->x86_capability & (X86_FEATURE_MCA | X86_FEATURE_MCE)) {
    printk(KERN_INFO "CPU%i: No machine check support available\n",
    smp_processor_id());
    return;
    }
    /* function code */
    }

    (ugly, because `mce_disabled == 1' check is even in gcc is likely by
    default). But changed my mind, due to violation of the coding style.
    Of course this my be no appropriate at all, but i'd like to bring
    this, if anyone would be like to discuss this.
    ____
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-10-09 19:21    [W:0.035 / U:1.568 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site