On Fri, Apr 07, 2017 at 06:47:43PM +0800, Jin Yao wrote:
> Perf already has support for disassembling the branch instruction
> and using the branch type for filtering. The patch just records
> the branch type in perf_branch_entry.
>
> Before recording, the patch converts the x86 branch classification
> to common branch classification and compute for checking if the
> branches cross 4K or 2MB areas. It's an approximate computing for
> crossing 4K page or 2MB page.
The changelog is completely empty of rationale. Why do we care?
Not having the binary is a very bad reason; you can't do much of
anything if that's missing.
> @@ -923,6 +933,84 @@ static int branch_type(unsigned long from, unsigned long
> to, int abort)
> return ret;
> }
>
> +static int
> +common_branch_type(int type, u64 from, u64 to)
> +{
> + int ret;
> +
> + type = type & (~(X86_BR_KERNEL | X86_BR_USER));
> +
> + switch (type) {
> + case X86_BR_CALL:
> + case X86_BR_ZERO_CALL:
> + ret = PERF_BR_CALL;
> + break;
> +
> + case X86_BR_RET:
> + ret = PERF_BR_RET;
> + break;
> +
> + case X86_BR_SYSCALL:
> + ret = PERF_BR_SYSCALL;
> + break;
> +
> + case X86_BR_SYSRET:
> + ret = PERF_BR_SYSRET;
> + break;
> +
> + case X86_BR_INT:
> + ret = PERF_BR_INT;
> + break;
> +
> + case X86_BR_IRET:
> + ret = PERF_BR_IRET;
> + break;
> +
> + case X86_BR_IRQ:
> + ret = PERF_BR_IRQ;
> + break;
> +
> + case X86_BR_ABORT:
> + ret = PERF_BR_FAR_BRANCH;
> + break;
> +
> + case X86_BR_JCC:
> + if (to > from)
> + ret = PERF_BR_JCC_FWD;
> + else
> + ret = PERF_BR_JCC_BWD;
> + break;
This seems like superfluous information; we already get to and from, so
this comparison is pointless.
The rest looks like something you can simpler implement using a lookup
table.
> +
> + case X86_BR_JMP:
> + ret = PERF_BR_JMP;
> + break;
> +
> + case X86_BR_IND_CALL:
> + ret = PERF_BR_IND_CALL;
> + break;
> +
> + case X86_BR_IND_JMP:
> + ret = PERF_BR_IND_JMP;
> + break;
> +
> + default:
> + ret = PERF_BR_NONE;
> + }
> +
> + return ret;
> +}
> +
> +static bool
> +cross_area(u64 addr1, u64 addr2, int size)
> +{
> + u64 align1, align2;
> +
> + align1 = addr1 & ~(size - 1);
> + align2 = addr2 & ~(size - 1);
> +
> + return (align1 != align2) ? true : false;
> +}
> +
> /*
> * implement actual branch filter based on user demand.
> * Hardware may not exactly satisfy that request, thus
> @@ -939,7 +1027,8 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
> bool compress = false;
>
> /* if sampling all branches, then nothing to filter */
> - if ((br_sel & X86_BR_ALL) == X86_BR_ALL)
> + if (((br_sel & X86_BR_ALL) == X86_BR_ALL) &&
> + ((br_sel & X86_BR_TYPE_SAVE) != X86_BR_TYPE_SAVE))
> return;
>
> for (i = 0; i < cpuc->lbr_stack.nr; i++) {
> @@ -960,6 +1049,21 @@ intel_pmu_lbr_filter(struct cpu_hw_events *cpuc)
> cpuc->lbr_entries[i].from = 0;
> compress = true;
> }
> +
> + if ((br_sel & X86_BR_TYPE_SAVE) == X86_BR_TYPE_SAVE) {
> + cpuc->lbr_entries[i].type = common_branch_type(type,
> + from,
> + to);
> + if (cross_area(from, to, AREA_2M))
> + cpuc->lbr_entries[i].cross = PERF_BR_CROSS_2M;
> + else if (cross_area(from, to, AREA_4K))
> + cpuc->lbr_entries[i].cross = PERF_BR_CROSS_4K;
> + else
> + cpuc->lbr_entries[i].cross = PERF_BR_CROSS_NONE;
This again is superfluous information; it is already fully contained in
to and from, which we have.
> + } else {
> + cpuc->lbr_entries[i].type = PERF_BR_NONE;
> + cpuc->lbr_entries[i].cross = PERF_BR_CROSS_NONE;
> + }
> }
>
> if (!compress)
> --
> 2.7.4
>
