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SubjectRe: [PATCH v2 2/7] iommu/vt-d: Multiple descriptors per qi_submit_sync()
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On 2020/4/15 16:18, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Wednesday, April 15, 2020 1:26 PM
>>
>> Extend qi_submit_sync() function to support multiple descriptors.
>>
>> Signed-off-by: Jacob Pan<jacob.jun.pan@linux.intel.com>
>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>> ---
>> drivers/iommu/dmar.c | 39 +++++++++++++++++++++++--------------
>> include/linux/intel-iommu.h | 1 +
>> 2 files changed, 25 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/iommu/dmar.c b/drivers/iommu/dmar.c
>> index bb42177e2369..61d049e91f84 100644
>> --- a/drivers/iommu/dmar.c
>> +++ b/drivers/iommu/dmar.c
>> @@ -1157,12 +1157,11 @@ static inline void reclaim_free_desc(struct
>> q_inval *qi)
>> }
>> }
>>
>> -static int qi_check_fault(struct intel_iommu *iommu, int index)
>> +static int qi_check_fault(struct intel_iommu *iommu, int index, int
>> wait_index)
>> {
>> u32 fault;
>> int head, tail;
>> struct q_inval *qi = iommu->qi;
>> - int wait_index = (index + 1) % QI_LENGTH;
>> int shift = qi_shift(iommu);
>>
>> if (qi->desc_status[wait_index] == QI_ABORT)
>> @@ -1234,12 +1233,12 @@ static int qi_check_fault(struct intel_iommu
>> *iommu, int index)
>> int qi_submit_sync(struct intel_iommu *iommu, struct qi_desc *desc,
>> unsigned int count, unsigned long options)
>> {
>> - int rc;
>> struct q_inval *qi = iommu->qi;
>> - int offset, shift, length;
>> struct qi_desc wait_desc;
>> int wait_index, index;
>> unsigned long flags;
>> + int offset, shift;
>> + int rc, i;
>>
>> if (!qi)
>> return 0;
>> @@ -1248,32 +1247,41 @@ int qi_submit_sync(struct intel_iommu *iommu,
>> struct qi_desc *desc,
>> rc = 0;
>>
>> raw_spin_lock_irqsave(&qi->q_lock, flags);
>> - while (qi->free_cnt < 3) {
>> + /*
>> + * Check if we have enough empty slots in the queue to submit,
>> + * the calculation is based on:
>> + * # of desc + 1 wait desc + 1 space between head and tail
>> + */
>> + while (qi->free_cnt < count + 2) {
>> raw_spin_unlock_irqrestore(&qi->q_lock, flags);
>> cpu_relax();
>> raw_spin_lock_irqsave(&qi->q_lock, flags);
>> }
>>
>> index = qi->free_head;
>> - wait_index = (index + 1) % QI_LENGTH;
>> + wait_index = (index + count) % QI_LENGTH;
>> shift = qi_shift(iommu);
>> - length = 1 << shift;
>>
>> - qi->desc_status[index] = qi->desc_status[wait_index] = QI_IN_USE;
>> + for (i = 0; i < count; i++) {
>> + offset = ((index + i) % QI_LENGTH) << shift;
>> + memcpy(qi->desc + offset, &desc[i], 1 << shift);
>> + qi->desc_status[(index + i) % QI_LENGTH] = QI_IN_USE;
>> + }
> what about doing one memcpy and leave the loop only for updating
> qi status?
>

One memcpy might cross the table boundary.

Best regards,
baolu

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