Messages in this thread | ![/](/images/icornerl.gif) | | Date | Mon, 5 Jun 2023 08:44:50 +0530 | Subject | Re: [PATCH V11 08/10] arm64/perf: Add struct brbe_regset helper functions | From | Anshuman Khandual <> |
| |
On 6/2/23 08:10, Namhyung Kim wrote: > On Tue, May 30, 2023 at 9:15 PM Anshuman Khandual > <anshuman.khandual@arm.com> 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> >> --- > > [SNIP] >> + >> +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; >> +} >> + >> +/* >> + * 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); > > I'm afraid it can overwrite some entries if nr_live is small > and nr_stored is big. Why not use memmove()?
nr_stored is first adjusted with nr_excess if both live and stored entries combined exceed the maximum branch records in the HW. I am wondering how it can override ?
> > Also I think it'd be simpler if you copy store to live. > It'll save copying live in the IRQ but it will copy the > whole content to store again for the sched switch.
But how that is better than the current scheme ?
| ![\](/images/icornerr.gif) |