[nvmewin] NVMe Queue entry number

[Robles, Raymond C]

Hi Wenqian,

Thank you for your inquiry. In the FindAdapter routine (in nvmeStd.c), the driver checks CAP.MQES and saves the value in pAE->InitInfo.IoQEntries (if the default or register override is smaller than CAP.MQES, it is saved instead). Within the function NVMeAllocIoQueues, there is loop that will iterate to create queue pairs based on the number of cpu cores.

In this loop, a call to NVMeAllocQueues is made. Just prior to this call, the value saved in pAE->InitInfo.IoQEntires is retrieved (stack variable “QEntres”) and passed in as the 3rd parameter. So, once the allocation is taking place where you mention below, the 3rd parameter of the function has already been checked against CAP.MQES. Also, per the NVMe spec sections 5.3 and 5.4 – Figures 33 and 37 (create completion queue and submission queue PRP 1), all queue memory must be “physically contiguous and memory page aligned”.

Thanks
Ray

From: nvmewin-bounces at lists.openfabrics.org [mailto:nvmewin-bounces at lists.openfabrics.org] On Behalf Of Wenqian Wu
Sent: Wednesday, February 11, 2015 4:58 PM
To: nvmewin at lists.openfabrics.org
Subject: [nvmewin] NVMe Queue entry number

Hi OFA driver member,

I have one question regarding the Queue entry size. The driver will allocate number of entries aligned to memory page (line877, nvmeInit.c), instead of the actual queue size controller supports (CAP.MQES). Controller can return error if host request more entries while ignoring controller's capability. I think as long as the base address is page aligned, there is no reason to make the entries number aligned to page boundary. Can this be considered a driver bug or is there any particular consideration?

Thanks,
Wenqian
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