From mboxrd@z Thu Jan 1 00:00:00 1970 From: saeed.bishara@gmail.com (saeed bishara) Date: Sun, 20 Jun 2010 06:49:56 -0500 Subject: [PATCH 1/2 v2] mv643xx_eth: use sw csum for big packets In-Reply-To: <20100614093237.GG14513@mail.wantstofly.org> References: <1276073483-17208-1-git-send-email-saeed@marvell.com> <20100610064330.GK1743@mail.wantstofly.org> <20100612083137.GO1743@mail.wantstofly.org> <20100614093237.GG14513@mail.wantstofly.org> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Mon, Jun 14, 2010 at 4:32 AM, Lennert Buytenhek wrote: > On Sun, Jun 13, 2010 at 10:38:10AM +0300, Saeed Bishara wrote: > >> >> >> @@ -2666,6 +2668,9 @@ static int >> >> >mv643xx_eth_shared_probe(struct platform_device *pdev) >> >> >> ? ? ? ? ?* Detect hardware parameters. >> >> >> ? ? ? ? ?*/ >> >> >> ? ? ? ? msp->t_clk = (pd != NULL && pd->t_clk != 0) ? pd->t_clk >> >> >: 133000000; >> >> >> + ? ? ? msp->tx_csum_limit = pd->tx_csum_limit ? >> >> >pd->tx_csum_limit : 9 * 1024; >> >> >> + ? ? ? /* add header count so we can compare against skb->len */ >> >> >> + ? ? ? msp->tx_csum_limit += ETH_HLEN; >> >> >> ? ? ? ? infer_hw_params(msp); >> >> > >> >> >Is the limit 9 * 1024 + 14 for the whole packet, or 9 * >> >1024 for the IP >> >> >part? >> >> >> >> the limit is for the IP part, but I thought that adding the >> >header length, then comparing agains skb->len will be the >> >same. What do you suggest? >> > >> >Right, but for the header length you take 14, while if to include VLAN >> >tags or DSA tags the header might actually be longer -- how does that >> >affect the ability of the hardware to compute the checksum? >> > >> >I.e. is the restriction "total packet length must be < N + 14 bytes" >> >or is it "the IP part must be < N bytes and it doesn't matter whether >> >there are VLAN tags or not"? >> >> It's the second option: "the IP part must be < N" regardless to the L2 header. > > Then I suppose you want to do something like: > > ? ? ? ?int hdr_len; > ? ? ? ?int tag_bytes; > > ? ? ? ?hdr_len = (void *)ip_hdr(skb) - (void *)skb->data; > ? ? ? ?tag_bytes = hdr_len - 4; that should be 14 instead of 4, right? > ? ? ? ?if (skb->len - hdr_len > the limit || unlikely(tag_bytes & ~12)) { > > (And then keep the limit as maximum number of bytes in the packet > starting from the IP header part.) ok. here is the updated patch: