On Wed, May 3, 2017 at 9:10 PM, Will Deacon <will.dea...@arm.com> wrote: > On Wed, May 03, 2017 at 04:33:57PM +0100, Robin Murphy wrote: >> 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? > > I asked that the timeout is only increased for the drain case, and that > we fix the issue here where we udelat if cons didn't move immediately: > > http://lists.infradead.org/pipermail/linux-arm-kernel/2017-April/503389.html > > but I don't think the patch above actually achieves any of that. > > Will
Sorry, I completely screwed up the spin poll above. Will resubmit. Thanks, Sunil. _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu