svn commit: r281280 - head/sys/dev/nvme

[Alexander Kabaev]

On Wed, 8 Apr 2015 21:46:19 +0000 (UTC)
Jim Harris <jimharris at FreeBSD.org> wrote:

> Author: jimharris
> Date: Wed Apr  8 21:46:18 2015
> New Revision: 281280
> URL: https://svnweb.freebsd.org/changeset/base/281280
> 
> Log:
>   nvme: fall back to a smaller MSI-X vector allocation if necessary
>   
>   Previously, if per-CPU MSI-X vectors could not be allocated,
>   nvme(4) would fall back to INTx with a single I/O queue pair.
>   This change will still fall back to a single I/O queue pair, but
>   allocate MSI-X vectors instead of reverting to INTx.
>   
>   MFC after:	1 week
>   Sponsored by:	Intel
> 
> Modified:
>   head/sys/dev/nvme/nvme_ctrlr.c
> 
> Modified: head/sys/dev/nvme/nvme_ctrlr.c
> ==============================================================================
> --- head/sys/dev/nvme/nvme_ctrlr.c	Wed Apr  8 21:10:13
> 2015	(r281279) +++ head/sys/dev/nvme/nvme_ctrlr.c	Wed
> Apr  8 21:46:18 2015	(r281280) @@ -1144,9 +1144,17 @@
> nvme_ctrlr_construct(struct nvme_control /* One vector per IO queue,
> plus one vector for admin queue. */ num_vectors =
> ctrlr->num_io_queues + 1; 
> -	if (pci_msix_count(dev) < num_vectors) {
> +	/*
> +	 * If we cannot even allocate 2 vectors (one for admin, one
> for
> +	 *  I/O), then revert to INTx.
> +	 */
> +	if (pci_msix_count(dev) < 2) {
>  		ctrlr->msix_enabled = 0;
>  		goto intx;
> +	} else if (pci_msix_count(dev) < num_vectors) {
> +		ctrlr->per_cpu_io_queues = FALSE;
> +		ctrlr->num_io_queues = 1;
> +		num_vectors = 2; /* one for admin, one for I/O */
>  	}
>  
>  	if (pci_alloc_msix(dev, &num_vectors) != 0) {

Huh, Linux just falls back to as many vectors as it can and just
allocates them between per-cpu queues in a round-robin manner. I think
is is a better approach than what we have here, would you consider it?
-- 
Alexander Kabaev
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