Re: [PATCH v2] xen/netfront: raise max number of slots in xennet_get_responses()

[David Miller]

From: Juergen Gross <jgross@xxxxxxxx>
Date: Tue, 12 Jun 2018 08:57:53 +0200

> The max number of slots used in xennet_get_responses() is set to
> MAX_SKB_FRAGS + (rx->status <= RX_COPY_THRESHOLD).
> 
> In old kernel-xen MAX_SKB_FRAGS was 18, while nowadays it is 17. This
> difference is resulting in frequent messages "too many slots" and a
> reduced network throughput for some workloads (factor 10 below that of
> a kernel-xen based guest).
> 
> Replacing MAX_SKB_FRAGS by XEN_NETIF_NR_SLOTS_MIN for calculation of
> the max number of slots to use solves that problem (tests showed no
> more messages "too many slots" and throughput was as high as with the
> kernel-xen based guest system).
> 
> Replace MAX_SKB_FRAGS-2 by XEN_NETIF_NR_SLOTS_MIN-1 in
> netfront_tx_slot_available() for making it clearer what is really being
> tested without actually modifying the tested value.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>

Applied, thanks.