Hi,
On 2/8/20 1:05 AM, Thomas Gleixner wrote:
Hans,
Hans de Goede <hdegoede@xxxxxxxxxx> writes:
@@ -120,11 +180,23 @@ unsigned long cpu_khz_from_msr(void)
rdmsr(MSR_FSB_FREQ, lo, hi);
index = lo & freq_desc->mask;
- /* Map CPU reference clock freq ID(0-7) to CPU reference clock freq(KHz) */
- freq = freq_desc->freqs[index];
-
- /* TSC frequency = maximum resolved freq * maximum resolved bus ratio */
- res = freq * ratio;
+ /*
+ * Note this also catches cases where the index points to an unpopulated
+ * part of muldiv, in that case the else will set freq and res to 0.
+ */
+ if (freq_desc->muldiv[index].divider) {
+ freq = DIV_ROUND_CLOSEST(TSC_REFERENCE_KHZ *
+ freq_desc->muldiv[index].multiplier,
+ freq_desc->muldiv[index].divider);
+ /* Multiply by ratio before the divide for better accuracy */
+ res = DIV_ROUND_CLOSEST(TSC_REFERENCE_KHZ *
+ freq_desc->muldiv[index].multiplier *
+ ratio,
+ freq_desc->muldiv[index].divider);
What about:
struct muldiv *md = &freq_desc->muldiv[index];
if (md->divider) {
tscref = TSC_REFERENCE_KHZ * md->multiplier;
freq = DIV_ROUND_CLOSEST(tscref, md->divider);
/*
* Multiplying by ratio before the division has better
* accuracy than just calculating freq * ratio
*/
res = DIV_ROUND_CLOSEST(tscref * ratio, md->divider);
Hmm?
That indeed looks nicer, I've prepared (and tested) a v4 with the
suggested change, I'll send out v4 right after this email.
Regards,
Hans
