Messages in this thread | ![/](/images/icornerl.gif) | | Date | Wed, 14 Jun 2023 10:44:38 +0530 | Subject | Re: [PATCH V11 08/10] arm64/perf: Add struct brbe_regset helper functions | From | Anshuman Khandual <> |
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On 6/13/23 22:47, Mark Rutland wrote: > 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.
I have changed both the places (in separate patches) with suggested loop structure.
> > 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.
There are indeed two places inside capture_brbe_regset() - one for each bank.
> > | 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))
It should test !_read_brbe_regset(&buf[idx], idx)) instead as the error case returns false.
> | 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;
Ditto.
> | } > | > | return idx; > | }
Will factor out a new helper __read_brbe_regset() from capture_brbe_regset().
> > ... 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]; > | }
Agreed.
> > ... 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.
Agreed, will drop copy_brbe_regset().
> >> +/* >> + * 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
Fixed these typos ^^^ ^^^
>> + * 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);
Should this compare be min() instead ? As all nr_live entries need to be moved starting store[0], there will be (nr_max - nr_live) entries left for initial stored entries movement, irrespective of how many of stored entries are actually present. Hence (nr_max - nr_live) acts as a cap on nr_stored value for this initial movement. But if nr_stored is smaller than nr_max - nr_live, it gets picked up.
> > /* 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); > }
Otherwise this makes sense and simpler, will rework.
> > ... or if we could save this oldest-first, we could make it a circular buffer > and avoid moving older entries.
Storing the youngest entries first is aligned with how perf branch stack sampling stores the entries in struct perf_sample_data which gets copied 'as is' from cpuc->branches->branch_stack. Hence, just keeping all these buffer in the same age order (youngest first in index 0) really makes sense. Although the above rework seems fine.
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