linux-kernel - Re: [PATCH v2] xen/netfront: raise max number of slots in xennet_get

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Message-Id: <20180612.154324.84720221873990983.davem@davemloft.net>
Date:   Tue, 12 Jun 2018 15:43:24 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     jgross@...e.com
Cc:     linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        netdev@...r.kernel.org, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v2] xen/netfront: raise max number of slots in
 xennet_get_responses()

From: Juergen Gross <jgross@...e.com>
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@...e.com>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>

Applied, thanks.