From: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
To: Jonathan Davies <jonathan.davies@citrix.com>,
netdev@vger.kernel.org, xen-devel@lists.xenproject.org,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Boris Ostrovsky <boris.ostrovsky@oracle.com>,
David Vrabel <david.vrabel@citrix.com>
Cc: Wei Liu <wei.liu2@citrix.com>
Subject: Re: [PATCH] xen-netfront: transmit fully GSO-sized packets
Date: Thu, 26 Mar 2015 17:14:08 +0300 [thread overview]
Message-ID: <55141430.9050309__42253.0639953495$1427379372$gmane$org@cogentembedded.com> (raw)
In-Reply-To: <1427368406-28084-1-git-send-email-jonathan.davies@citrix.com>
Hello.
On 3/26/2015 2:13 PM, Jonathan Davies wrote:
> xen-netfront limits transmitted skbs to be at most 44 segments in size. However,
> GSO permits up to 65536 bytes, which means a maximum of 45 segments of 1448
> bytes each. This slight reduction in the size of packets means a slight loss in
> efficiency.
> Since c/s 9ecd1a75d, xen-netfront sets gso_max_size to
c/s == commit?
Please also specify that commit's summary line in parens.
> XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER,
> where XEN_NETIF_MAX_TX_SIZE is 65535 bytes.
> The calculation used by tcp_tso_autosize (and also tcp_xmit_size_goal since c/s
> 6c09fa09d) in determining when to split an skb into two is
Likewise.
> sk->sk_gso_max_size - 1 - MAX_TCP_HEADER.
> So the maximum permitted size of an skb is calculated to be
> (XEN_NETIF_MAX_TX_SIZE - MAX_TCP_HEADER) - 1 - MAX_TCP_HEADER.
> Intuitively, this looks like the wrong formula -- we don't need two TCP headers.
> Instead, there is no need to deviate from the default gso_max_size of 65536 as
> this already accommodates the size of the header.
> Currently, the largest skb transmitted by netfront is 63712 bytes (44 segments
> of 1448 bytes each), as observed via tcpdump. This patch makes netfront send
> skbs of up to 65160 bytes (45 segments of 1448 bytes each).
> Fixes: 9ecd1a75d977 ("xen-netfront: reduce gso_max_size to account for max TCP header")
Ah, here's the summary for the first mentioned commit...
> Signed-off-by: Jonathan Davies <jonathan.davies@citrix.com>
WBR, Sergei
next prev parent reply other threads:[~2015-03-26 14:14 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-26 11:13 [PATCH] xen-netfront: transmit fully GSO-sized packets Jonathan Davies
2015-03-26 12:05 ` Eric Dumazet
2015-03-26 12:05 ` Eric Dumazet
2015-03-26 15:08 ` Jonathan Davies
2015-03-26 15:08 ` Jonathan Davies
2015-03-30 13:46 ` Wei Liu
2015-03-31 9:16 ` Jonathan Davies
2015-03-31 9:16 ` Jonathan Davies
2015-03-30 13:46 ` Wei Liu
2015-03-26 14:14 ` Sergei Shtylyov [this message]
2015-03-26 14:14 ` Sergei Shtylyov
-- strict thread matches above, loose matches on Subject: below --
2015-03-26 11:13 Jonathan Davies
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