On 27/04/17 12:13, sunil.kovv...@gmail.com wrote: > From: Sunil Goutham <sgout...@cavium.com> > > Modified polling on CMDQ consumer similar to how polling is done for TLB SYNC > completion in SMMUv2 driver. Code changes are done with reference to > > 8513c8930069 iommu/arm-smmu: Poll for TLB sync completion more effectively > > Poll timeout has been increased which addresses issue of 100us timeout not > sufficient, when command queue is full with TLB invalidation commands. > > Signed-off-by: Sunil Goutham <sgout...@cavium.com> > Signed-off-by: Geetha <gak...@cavium.com> > --- > drivers/iommu/arm-smmu-v3.c | 15 ++++++++++++--- > 1 file changed, 12 insertions(+), 3 deletions(-) > > diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c > index d412bdd..34599d4 100644 > --- a/drivers/iommu/arm-smmu-v3.c > +++ b/drivers/iommu/arm-smmu-v3.c > @@ -379,6 +379,9 @@ > #define CMDQ_SYNC_0_CS_NONE (0UL << CMDQ_SYNC_0_CS_SHIFT) > #define CMDQ_SYNC_0_CS_SEV (2UL << CMDQ_SYNC_0_CS_SHIFT) > > +#define CMDQ_DRAIN_TIMEOUT_US 1000 > +#define CMDQ_SPIN_COUNT 10 > + > /* Event queue */ > #define EVTQ_ENT_DWORDS 4 > #define EVTQ_MAX_SZ_SHIFT 7 > @@ -737,7 +740,8 @@ static void queue_inc_prod(struct arm_smmu_queue *q) > */ > static int queue_poll_cons(struct arm_smmu_queue *q, bool drain, bool wfe) > { > - ktime_t timeout = ktime_add_us(ktime_get(), ARM_SMMU_POLL_TIMEOUT_US); > + ktime_t timeout = ktime_add_us(ktime_get(), CMDQ_DRAIN_TIMEOUT_US); > + unsigned int spin_cnt, delay = 1; > > while (queue_sync_cons(q), (drain ? !queue_empty(q) : queue_full(q))) { > if (ktime_compare(ktime_get(), timeout) > 0) > @@ -746,8 +750,13 @@ static int queue_poll_cons(struct arm_smmu_queue *q, > bool drain, bool wfe) > if (wfe) { > wfe(); > } else { > - cpu_relax(); > - udelay(1); > + for (spin_cnt = 0; > + spin_cnt < CMDQ_SPIN_COUNT; spin_cnt++) { > + cpu_relax(); > + continue; > + } > + udelay(delay); > + delay *= 2;
Sorry, I can't make sense of this. The referenced commit uses the spin loop to poll opportunistically a few times before delaying. This loop just adds a short open-coded udelay to an exponential udelay, and it's not really clear that that's any better than a fixed udelay (especially as the two cases in which we poll are somewhat different). What's wrong with simply increasing the timeout value alone? Robin. > } > } > > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu