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Re: [PATCH-for-6.0 v2 25/25] block/nvme: Simplify Completion Queue Comma
From: |
Philippe Mathieu-Daudé |
Subject: |
Re: [PATCH-for-6.0 v2 25/25] block/nvme: Simplify Completion Queue Command Identifier field use |
Date: |
Fri, 30 Oct 2020 15:53:54 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 |
On 10/30/20 3:00 PM, Stefan Hajnoczi wrote:
> On Thu, Oct 29, 2020 at 10:33:06AM +0100, Philippe Mathieu-Daudé wrote:
>> The "Completion Queue Entry: DW 2" describes it as:
>>
>> This identifier is assigned by host software when
>> the command is submitted to the Submission
>>
>> As the is just an opaque cookie, it is pointless to byte-swap it.
>>
>> Suggested-by: Keith Busch <kbusch@kernel.org>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>> block/nvme.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/block/nvme.c b/block/nvme.c
>> index a06a188d530..e7723c42a6d 100644
>> --- a/block/nvme.c
>> +++ b/block/nvme.c
>> @@ -344,7 +344,7 @@ static inline int nvme_translate_error(const NvmeCqe *c)
>> trace_nvme_error(le32_to_cpu(c->result),
>> le16_to_cpu(c->sq_head),
>> le16_to_cpu(c->sq_id),
>> - le16_to_cpu(c->cid),
>> + c->cid,
>> le16_to_cpu(status));
>> }
>> switch (status) {
>> @@ -401,7 +401,7 @@ static bool nvme_process_completion(NVMeQueuePair *q)
>> if (!q->cq.head) {
>> q->cq_phase = !q->cq_phase;
>> }
>> - cid = le16_to_cpu(c->cid);
>> + cid = c->cid;
>> if (cid == 0 || cid > NVME_QUEUE_SIZE) {
>> warn_report("NVMe: Unexpected CID in completion queue:
>> %"PRIu32", "
>> "queue size: %u", cid, NVME_QUEUE_SIZE);
>> @@ -469,7 +469,7 @@ static void nvme_submit_command(NVMeQueuePair *q,
>> NVMeRequest *req,
>> assert(!req->cb);
>> req->cb = cb;
>> req->opaque = opaque;
>> - cmd->cid = cpu_to_le16(req->cid);
>> + cmd->cid = req->cid;
>>
>> trace_nvme_submit_command(q->s, q->index, req->cid);
>> nvme_trace_command(cmd);
>
> Eliminating the byteswap is safe but this patch makes the code
> confusing, as I mentioned previously.
>
> Please use a comment or macro to mark this field native endian. It's not
> obvious to the reader that we can skip the byteswap here.
>
> Otherwise it will confuse readers into adding the byteswap back, not
> using byteswapping in other places where it is needed, etc.
OK. (This patch is for 6.0 anyway, I included because it was
following the previous patch in its previous version).
>
> Thanks,
> Stefan
>
- [PATCH-for-5.2 v2 19/25] block/nvme: Change size and alignment of IDENTIFY response buffer, (continued)
- [PATCH-for-5.2 v2 19/25] block/nvme: Change size and alignment of IDENTIFY response buffer, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 18/25] block/nvme: Correct minimum device page size, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 20/25] block/nvme: Change size and alignment of queue, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 21/25] block/nvme: Change size and alignment of prp_list_pages, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 22/25] block/nvme: Align iov's va and size on host page size, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 23/25] block/nvme: Fix use of write-only doorbells page on Aarch64 arch, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-5.2 v2 24/25] block/nvme: Fix nvme_submit_command() on big-endian host, Philippe Mathieu-Daudé, 2020/10/29
- [PATCH-for-6.0 v2 25/25] block/nvme: Simplify Completion Queue Command Identifier field use, Philippe Mathieu-Daudé, 2020/10/29