Messages in this thread | | | Date | Tue, 13 Jun 2023 18:17:51 +0100 | From | Mark Rutland <> | Subject | Re: [PATCH V11 08/10] arm64/perf: Add struct brbe_regset helper functions |
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On Wed, May 31, 2023 at 09:34:26AM +0530, Anshuman Khandual wrote: > The primary abstraction level for fetching branch records from BRBE HW has > been changed as 'struct brbe_regset', which contains storage for all three > BRBE registers i.e BRBSRC, BRBTGT, BRBINF. Whether branch record processing > happens in the task sched out path, or in the PMU IRQ handling path, these > registers need to be extracted from the HW. Afterwards both live and stored > sets need to be stitched together to create final branch records set. This > adds required helper functions for such operations. > > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Tested-by: James Clark <james.clark@arm.com> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com> > --- > drivers/perf/arm_brbe.c | 163 ++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 163 insertions(+) > > diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c > index 484842d8cf3e..759db681d673 100644 > --- a/drivers/perf/arm_brbe.c > +++ b/drivers/perf/arm_brbe.c > @@ -44,6 +44,169 @@ static void select_brbe_bank(int bank) > isb(); > } > > +/* > + * This scans over BRBE register banks and captures individual branch reocrds > + * [BRBSRC, BRBTGT, BRBINF] into a pre-allocated 'struct brbe_regset' buffer, > + * until an invalid one gets encountered. The caller for this function needs > + * to ensure BRBE is an appropriate state before the records can be captured. > + */ > +static int capture_brbe_regset(struct brbe_hw_attr *brbe_attr, struct brbe_regset *buf) > +{ > + int loop1_idx1, loop1_idx2, loop2_idx1, loop2_idx2; > + int idx, count; > + > + loop1_idx1 = BRBE_BANK0_IDX_MIN; > + if (brbe_attr->brbe_nr <= BRBE_BANK_MAX_ENTRIES) { > + loop1_idx2 = brbe_attr->brbe_nr - 1; > + loop2_idx1 = BRBE_BANK1_IDX_MIN; > + loop2_idx2 = BRBE_BANK0_IDX_MAX; > + } else { > + loop1_idx2 = BRBE_BANK0_IDX_MAX; > + loop2_idx1 = BRBE_BANK1_IDX_MIN; > + loop2_idx2 = brbe_attr->brbe_nr - 1; > + } > + > + select_brbe_bank(BRBE_BANK_IDX_0); > + for (idx = 0, count = loop1_idx1; count <= loop1_idx2; idx++, count++) { > + buf[idx].brbinf = get_brbinf_reg(idx); > + /* > + * There are no valid entries anymore on the buffer. > + * Abort the branch record processing to save some > + * cycles and also reduce the capture/process load > + * for the user space as well. > + */ > + if (brbe_invalid(buf[idx].brbinf)) > + return idx; > + > + buf[idx].brbsrc = get_brbsrc_reg(idx); > + buf[idx].brbtgt = get_brbtgt_reg(idx); > + } > + > + select_brbe_bank(BRBE_BANK_IDX_1); > + for (count = loop2_idx1; count <= loop2_idx2; idx++, count++) { > + buf[idx].brbinf = get_brbinf_reg(idx); > + /* > + * There are no valid entries anymore on the buffer. > + * Abort the branch record processing to save some > + * cycles and also reduce the capture/process load > + * for the user space as well. > + */ > + if (brbe_invalid(buf[idx].brbinf)) > + return idx; > + > + buf[idx].brbsrc = get_brbsrc_reg(idx); > + buf[idx].brbtgt = get_brbtgt_reg(idx); > + } > + return idx; > +}
As with __armv8pmu_branch_read(), the loop conditions are a bit hard to follow, and I believe that can be rewritten along the lines of the suggestion there.
Looking at this, we now have a couple of places that will try to read the registers for an individual record, so it probably makes sense to facotr that into a helper, e.g.
| static bool __read_brbe_regset(struct brbe_regset *entry, int idx) | { | u64 brbinf = get_brbinf_reg(idx); | | if (brbe_invalid(brbinf)) | return false; | | entry->brbinf = brbinf; | entry->brbsrc = get_brbsrc_reg(idx); | entry->brbtgt = get_brbtgt_reg(idx); | | return true; | }
... which can be used here, e.g.
| /* | * Capture all records before the first invalid record, and return the number | * of records captured. | */ | static int capture_brbe_regset(struct brbe_hw_attr *brbe_attr, struct brbe_regset *buf) | { | | int nr_entries = brbe_attr->brbe_nr; | int idx = 0; | | select_brbe_bank(BRBE_BANK_IDX_0); | while (idx < nr_entries && IDX < BRBE_BANK0_IDX_MAX) { | if (__read_brbe_regset(&buf[idx], idx)) | return idx; | } | | select_brbe_bank(BRBE_BANK_IDX_1); | while (idx < nr_entries && IDX < BRBE_BANK1_IDX_MAX) { | if (__read_brbe_regset(&buf[idx], idx)) | return idx; | } | | return idx; | }
... and could be used to implement capture_branch_entry() in the patch before this.
> +static inline void copy_brbe_regset(struct brbe_regset *src, int src_idx, > + struct brbe_regset *dst, int dst_idx) > +{ > + dst[dst_idx].brbinf = src[src_idx].brbinf; > + dst[dst_idx].brbsrc = src[src_idx].brbsrc; > + dst[dst_idx].brbtgt = src[src_idx].brbtgt; > +}
C can do struct assignment, so this is the same as:
| static inline void copy_brbe_regset(struct brbe_regset *src, int src_idx, | struct brbe_regset *dst, int dst_idx) | { | dst[dst_idx] = src[src_idx]; | }
... and given that, it would be simpler and clearer to have that directly in the caller, so I don't think we need this helper function.
> +/* > + * This function concatenates branch records from stored and live buffer > + * up to maximum nr_max records and the stored buffer holds the resultant > + * buffer. The concatenated buffer contains all the branch records from > + * the live buffer but might contain some from stored buffer considering > + * the maximum combined length does not exceed 'nr_max'. > + * > + * Stored records Live records > + * ------------------------------------------------^ > + * | S0 | L0 | Newest | > + * --------------------------------- | > + * | S1 | L1 | | > + * --------------------------------- | > + * | S2 | L2 | | > + * --------------------------------- | > + * | S3 | L3 | | > + * --------------------------------- | > + * | S4 | L4 | nr_max > + * --------------------------------- | > + * | | L5 | | > + * --------------------------------- | > + * | | L6 | | > + * --------------------------------- | > + * | | L7 | | > + * --------------------------------- | > + * | | | | > + * --------------------------------- | > + * | | | Oldest | > + * ------------------------------------------------V > + * > + * > + * S0 is the newest in the stored records, where as L7 is the oldest in > + * the live reocords. Unless the live buffer is detetcted as being full > + * thus potentially dropping off some older records, L7 and S0 records > + * are contiguous in time for a user task context. The stitched buffer > + * here represents maximum possible branch records, contiguous in time. > + * > + * Stored records Live records > + * ------------------------------------------------^ > + * | L0 | L0 | Newest | > + * --------------------------------- | > + * | L0 | L1 | | > + * --------------------------------- | > + * | L2 | L2 | | > + * --------------------------------- | > + * | L3 | L3 | | > + * --------------------------------- | > + * | L4 | L4 | nr_max > + * --------------------------------- | > + * | L5 | L5 | | > + * --------------------------------- | > + * | L6 | L6 | | > + * --------------------------------- | > + * | L7 | L7 | | > + * --------------------------------- | > + * | S0 | | | > + * --------------------------------- | > + * | S1 | | Oldest | > + * ------------------------------------------------V > + * | S2 | <----| > + * ----------------- | > + * | S3 | <----| Dropped off after nr_max > + * ----------------- | > + * | S4 | <----| > + * ----------------- > + */ > +static int stitch_stored_live_entries(struct brbe_regset *stored, > + struct brbe_regset *live, > + int nr_stored, int nr_live, > + int nr_max) > +{ > + int nr_total, nr_excess, nr_last, i; > + > + nr_total = nr_stored + nr_live; > + nr_excess = nr_total - nr_max; > + > + /* Stored branch records in stitched buffer */ > + if (nr_live == nr_max) > + nr_stored = 0; > + else if (nr_excess > 0) > + nr_stored -= nr_excess; > + > + /* Stitched buffer branch records length */ > + if (nr_total > nr_max) > + nr_last = nr_max; > + else > + nr_last = nr_total; > + > + /* Move stored branch records */ > + for (i = 0; i < nr_stored; i++) > + copy_brbe_regset(stored, i, stored, nr_last - nr_stored - 1 + i); > + > + /* Copy live branch records */ > + for (i = 0; i < nr_live; i++) > + copy_brbe_regset(live, i, stored, i); > + > + return nr_last; > +}
I think this can be written more simply as something like:
static int stitch_stored_live_entries(struct brbe_regset *stored, struct brbe_regset *live, int nr_stored, int nr_live, int nr_max) { int nr_move = max(nr_stored, nr_max - nr_live);
/* Move the tail of the buffer to make room for the new entries */ memmove(&stored[nr_live], &stored[0], nr_move * sizeof(*stored));
/* Copy the new entries into the head of the buffer */ memcpy(stored[0], &live[0], nr_live * sizeof(*stored));
/* Return the number of entries in the stitched buffer */ return min(nr_live + nr_stored, nr_max); }
... or if we could save this oldest-first, we could make it a circular buffer and avoid moving older entries.
Thanks, Mark.
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