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    SubjectRe: [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs
    Date
    On Thu, May 25 2023 at 01:56, Michael Ellerman wrote:
    > There is a hook which allows arch code to control how many threads per

    Can you please write out architecture in changelogs and comments?

    I know 'arch' is commonly used but while my brain parser tolerates
    'arch_' prefixes it raises an exception on 'arch' in prose as 'arch' is
    a regular word with a completely different meaning. Changelogs and
    comments are not space constraint.

    > @@ -2505,20 +2505,38 @@ __store_smt_control(struct device *dev, struct device_attribute *attr,
    > if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
    > return -ENODEV;
    >
    > - if (sysfs_streq(buf, "on"))
    > + if (sysfs_streq(buf, "on")) {
    > ctrlval = CPU_SMT_ENABLED;
    > - else if (sysfs_streq(buf, "off"))
    > + num_threads = cpu_smt_max_threads;
    > + } else if (sysfs_streq(buf, "off")) {
    > ctrlval = CPU_SMT_DISABLED;
    > - else if (sysfs_streq(buf, "forceoff"))
    > + num_threads = 1;
    > + } else if (sysfs_streq(buf, "forceoff")) {
    > ctrlval = CPU_SMT_FORCE_DISABLED;
    > - else
    > + num_threads = 1;
    > + } else if (kstrtoint(buf, 10, &num_threads) == 0) {
    > + if (num_threads == 1)
    > + ctrlval = CPU_SMT_DISABLED;
    > + else if (num_threads > 1 && topology_smt_threads_supported(num_threads))
    > + ctrlval = CPU_SMT_ENABLED;
    > + else
    > + return -EINVAL;
    > + } else {
    > return -EINVAL;
    > + }
    >
    > ret = lock_device_hotplug_sysfs();
    > if (ret)
    > return ret;
    >
    > - if (ctrlval != cpu_smt_control) {
    > + orig_threads = cpu_smt_num_threads;
    > + cpu_smt_num_threads = num_threads;
    > +
    > + if (num_threads > orig_threads) {
    > + ret = cpuhp_smt_enable();
    > + } else if (num_threads < orig_threads) {
    > + ret = cpuhp_smt_disable(ctrlval);
    > + } else if (ctrlval != cpu_smt_control) {
    > switch (ctrlval) {
    > case CPU_SMT_ENABLED:
    > ret = cpuhp_smt_enable();

    This switch case does not make sense anymore.

    The only situation which reaches this is when the control value goes
    from CPU_SMT_DISABLED to CPU_SMT_FORCE_DISABLED because that's not
    changing the number of threads.

    So something like this is completely sufficient:

    if (num_threads > orig_threads)
    ret = cpuhp_smt_enable();
    else if (num_threads < orig_threads || ctrval == CPU_SMT_FORCE_DISABLED)
    ret = cpuhp_smt_disable(ctrlval);

    No?

    Thanks,

    tglx

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