[PATCH v4 RFC] nvme: improve performance for virtual NVMe devices

[Helen Koike]

On 2017-03-17 07:28 PM, Keith Busch wrote:
> On Fri, Mar 17, 2017 at 06:44:59PM -0300, Helen Koike wrote:
> > diff --git a/drivers/nvme/host/Kconfig b/drivers/nvme/host/Kconfig
> > index 90745a6..7ada6f3 100644
> > --- a/drivers/nvme/host/Kconfig
> > +++ b/drivers/nvme/host/Kconfig
> > @@ -59,4 +59,13 @@ config NVME_FC
> >        To configure a NVMe over Fabrics controller use the nvme-cli tool
> >        from https://github.com/linux-nvme/nvme-cli.
> >
> > +config NVME_DBBUF
> > +    bool "NVM Express Doorbell Buffer Config Command"
> > +    depends on NVME_CORE
> > +    ---help---
> > +      This provides support for the Doorbell Buffer Config Command, which
> > +      reduces the number of required MMIOs to ring doorbells, improving
> > +      performance for virtualised environments where MMIO causes a high
> > +      overhead.
> > +
> >        If unsure, say N.
>
> It looks like you took the last line from NVME_FC's help. But I don't
> think this capabilty should enabled through kernel config, though. Just
> have the driver react based on the device's advertised capabilities, ya?
>

The advantage is that you can chose to not use the feature (not sure if it has any usecase) and reduce the code size if unused. But the code is really small. I'll remove CONF_NVME_DBBUF then and send another version, the code will be much cleaner imho.

Helen