Return-path: Received: from mail-ie0-f171.google.com ([209.85.223.171]:36262 "EHLO mail-ie0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753004AbaILHqX (ORCPT ); Fri, 12 Sep 2014 03:46:23 -0400 Received: by mail-ie0-f171.google.com with SMTP id y20so422794ier.30 for ; Fri, 12 Sep 2014 00:46:22 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <54125652.7060205@netcommwireless.com> References: <540FA8D9.2070803@netcommwireless.com> <54100F0E.8030204@broadcom.com> <54125652.7060205@netcommwireless.com> Date: Fri, 12 Sep 2014 09:46:22 +0200 Message-ID: (sfid-20140912_094632_457699_B65DB276) Subject: Re: Not reaching optimum speeds with IEEE 802.11n From: Helmut Schaa To: Sourav Cc: Arend van Spriel , linux-wireless Content-Type: text/plain; charset=UTF-8 Sender: linux-wireless-owner@vger.kernel.org List-ID: On Fri, Sep 12, 2014 at 4:11 AM, Sourav wrote: > On 11/09/14 00:14, Helmut Schaa wrote: >> >> On Wed, Sep 10, 2014 at 10:42 AM, Arend van Spriel >> wrote: >>> >>> On 09/10/14 03:26, Sourav wrote: >>>> >>>> We are using Ralink chip Rt3072L (using rt2800usb drivers rt2800usb.c), >> >> The Ralink USB hardware is quite bad in reporting TX status and as >> such minstrel_ht cannot do proper rate selection. >> If you watch the rc stats at >> >> /sys/kernel/debug/ieee80211/phy0/netdev\:wlan0-0/stations/xx:xx:xx:xx:xx:xx/rc_stats >> you might see a lot of rate selection "hopping". >> >> Regards. >> Helmut > > please take a look at the attachments.... the first one shows the rc_stats > and iperf stats side by side on the router(iperf is running in client mode > in the router).....the second attachment is from a laptop which is running > iperf in server mode. > > I don't see a lot of rate "hopping" in the rc_stats file, (T,t and P) rates > are pretty much stable.... yet there is a big difference between those rates > and the throughput using iperf...... Indeed, rc_stats looks acceptable. > when you say "Ralink USB hardware is quite bad in reporting TX status", do > you mean that the HW reports less tx rate to minstrel_ht and so its rate > calculation is screwed up? The HW sometimes does not report the status of transmitted frames correctly. The TX status register is a FIFO of 16 (or similar) elements and if the driver is not reading it "fast enough" the FIFO will overflow :( at least that was the point when I was looking at the ralink hardware last time. Not sure if something changed recently. > Can you please let me know the section of code inside Rc_80211_minstrel_ht.c > (or somewhere else) which deals with getting the tx rate from ralink HW? There is no special code in minstrel(_ht) in regard to rt2x00. Are you able able to get some statistics on the receiver side (your windows machine) regarding TX rates and AMPDU lengths? Helmut