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Re: [PATCH v3 4/4] hw/nvme: add polling support
From: |
Klaus Jensen |
Subject: |
Re: [PATCH v3 4/4] hw/nvme: add polling support |
Date: |
Fri, 4 Nov 2022 07:32:12 +0100 |
On Nov 3 21:19, Jinhao Fan wrote:
> On 11/3/2022 8:10 PM, Klaus Jensen wrote:
> > I agree that the spec is a little unclear on this point. In any case, in
> > Linux, when the driver has decided that the sq tail must be updated,
> > it will use this check:
> >
> > (new_idx - event_idx - 1) < (new_idx - old)
>
> When eventidx is already behind, it's like:
>
> 0
> 1 <- event_idx
> 2 <- old
> 3 <- new_idx
> 4
> .
> .
> .
>
> In this case, (new_idx - event_idx - 1) = 3-1-1 = 1 >= (new_idx - old) =
> 3-2=1, so the host won't update sq tail. Where am I wrong in this example?
>
That becomes 1 >= 1, i.e. "true". So this will result in the driver
doing an mmio doorbell write.
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