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Date: Fri, 27 Feb 2015 10:17:59 +0100 From: Oliver Neukum <oliver@...kum.org> To: Bjørn Mork <bjorn@...k.no> Cc: Ben Hutchings <ben.hutchings@...ethink.co.uk>, netdev@...r.kernel.org, ct-linux-kernel <linux-kernel@...ethink.co.uk>, linux-usb@...r.kernel.org, Sami Farin <hvtaifwkbgefbaei@...il.com>, Aleksander Morgado <aleksander@...ksander.es> Subject: Re: [RFC][PATCH] usbnet: Fix tx_bytes statistic running backward in cdc_ncm On Fri, 2015-02-27 at 10:12 +0100, Bjørn Mork wrote: > Ben Hutchings <ben.hutchings@...ethink.co.uk> writes: > > > cdc_ncm disagrees with usbnet about how much framing overhead should > > be counted in the tx_bytes statistics, and tries 'fix' this by > > decrementing tx_bytes on the transmit path. But statistics must never > > be decremented except due to roll-over; this will thoroughly confuse > > user-space. Also, tx_bytes is only incremented by usbnet in the > > completion path. > > > > Fix this by requiring drivers that set FLAG_MULTI_FRAME to set a > > tx_bytes delta along with the tx_packets count. > > > > Signed-off-by: Ben Hutchings <ben.hutchings@...ethink.co.uk> > > --- > > I noticed this bug while trying to fix the tx_packets statistic in asix. > > It depends on the patch I just sent for that. I don't have any hardware > > to test this with, or any need to make it work. If you want this fix, > > please test and re-submit it yoursef. > > I tested this on an MBIM device, and it worked perfectly as-is. Please > submit it without the RFC prefix. This fixes a real and reported > problem with the cdc_ncm driver, so I'd claim it's "net" material along > with a stable Cc and > > Fixes: beeecd42c3b4 ("net: cdc_ncm/cdc_mbim: adding NCM protocol statistics") > > But you and David decide that, of course... > > > Fixing this was actually on my TODO-list after a recent report showing > one of the problems with the previous hack: The decremented tx_bytes > counter was never corrected if the URB transmission failed, possibly > ending up with a negative (i.e. very large since it is unsigned) > tx_bytes counter. > > Thanks a lot. I didn't know how to do this without introducing a new > callback or something. Your solutions is very nice, and so obvious when > I see it. Just brilliant :-) > > Tested-by: Bjørn Mork <bjorn@...k.no> > > And you might also want (if this is OK for Sami): > > Reported-by: Sami Farin <hvtaifwkbgefbaei@...il.com> Acked-by: Oliver Neukum <oliver@...kum.org> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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