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Date: Mon, 21 Jan 2013 23:36:49 +0100 From: Bjørn Mork <bjorn@...k.no> To: Alexey ORISHKO <alexey.orishko@...ricsson.com> Cc: "netdev\@vger.kernel.org" <netdev@...r.kernel.org>, "linux-usb\@vger.kernel.org" <linux-usb@...r.kernel.org>, Greg Suarez <gsuarez@...thmicro.com>, Oliver Neukum <oneukum@...e.de>, Alexey Orishko <alexey.orishko@...il.com> Subject: Re: [PATCH net 2/3] net: cdc_mbim: send ZLP after max sized NTBs Alexey ORISHKO <alexey.orishko@...ricsson.com> writes: >> -----Original Message----- >> From: Bjørn Mork [mailto:bjorn@...k.no] >> >> We normally avoid sending ZLPs by padding NTBs with a zero byte if the >> NTB is shorter than dwNtbOutMaxSize, resulting in a short USB packet >> instead of a ZLP. But in the case where the NTB length is exactly >> dwNtbOutMaxSize and this is an exact multiplum of wMaxPacketSize, then >> we must send a ZLP. >> >> This fixes an issue seen on a Sierra Wireless MC7710 device where the >> transmission would fail whenever we ended up padding the NTBs to max >> size. > > If you add ZLP for NTBs of dwNtbOutMaxSize, you are heavily affecting CPU > load, increasing interrupt load by factor of 2 in high load traffic > scenario and possibly decreasing throughput for all other devices > which behaves correctly. > > Why should others pay for Sierra Wireless fault? No, they shouldn't. > At least, do check VID/PID in usbnet and send ZLP only for malfunctioning > devices. Yes, this would be easy to implement by simply creating a vendor/device specific entry in cdc_mbim. But I do worry that this isn't Sierra Wireless fault, but Qualcomms fault. SW are using Qualcomm firmware to do the low level stuff, and I know the Qualcomm firmware implement MBIM functionality so it may very well be the one to blame (I don't know this for sure, and I have no idea how to verify it). If this is correct than we can expect hundreds of devices needing a device specific entry in a year or two. That's not what I was looking forward to with a class driver like cdc_mbim. And I still believe that there is reason to ask if this is really a fault at all. I don't know if this is particularily useful, but here is an usbmon extract from the driver without the extra ZLP fix: ffff88022aef3d40 3883111197 S Bo:8:005:1 -115 4096 = 4e434d48 0c000600 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff880213f2d2c0 3883111233 S Bi:8:005:2 -115 16384 < ffff8802274eab40 3883111255 S Bi:8:005:2 -115 16384 < ffff88022fd65980 3883111276 S Bi:8:005:2 -115 16384 < ffff880204351440 3883111297 S Bi:8:005:2 -115 16384 < ffff880213f2d8c0 3883111317 S Bi:8:005:2 -115 16384 < ffff88022aef3d40 3883111460 C Bo:8:005:1 0 4096 > ffff880204351e00 3883965516 S Bo:8:005:1 -115 4096 = 4e434d48 0c000700 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff880204351e00 3883965849 C Bo:8:005:1 0 4096 > ffff880204351e00 3884973428 S Bo:8:005:1 -115 4096 = 4e434d48 0c000800 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff880204351e00 3884973752 C Bo:8:005:1 0 4096 > ffff880204351d40 3885981392 S Bo:8:005:1 -115 4096 = 4e434d48 0c000900 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff880204351d40 3885981638 C Bo:8:005:1 0 4096 > ffff880231b128c0 3886989391 S Bo:8:005:1 -115 4096 = 4e434d48 0c000a00 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff880231b128c0 3886989622 C Bo:8:005:1 0 4096 > ffff8802041d8a40 3887997401 S Bo:8:005:1 -115 4096 = 4e434d48 0c000b00 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff8802041d8a40 3887997675 C Bo:8:005:1 0 4096 > ffff8802041d8a40 3889005720 S Bo:8:005:1 -115 4096 = 4e434d48 0c000c00 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff8802041d8a40 3889006019 C Bo:8:005:1 0 4096 > ffff8802041d8c80 3890013428 S Bo:8:005:1 -115 4096 = 4e434d48 0c000d00 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff8802041d8c80 3890013784 C Bo:8:005:1 0 4096 > ffff880213f2d2c0 3892433962 C Bi:8:005:2 -104 0 ffff8802274eab40 3892434032 C Bi:8:005:2 -104 0 ffff88022fd65980 3892434078 C Bi:8:005:2 -104 0 ffff880204351440 3892434126 C Bi:8:005:2 -104 0 ffff880213f2d8c0 3892434172 C Bi:8:005:2 -104 0 same driver, with smaller packets keeping the NTB size below the magic limit: ffff88022b1de200 3896794916 S Bi:8:005:2 -115 16384 < ffff88022767d780 3896794928 C Bo:8:005:1 0 262 > ffff88022b1de140 3896794948 S Bi:8:005:2 -115 16384 < ffff88022767d780 3896794971 S Bi:8:005:2 -115 16384 < ffff88022b1deb00 3896794995 S Bi:8:005:2 -115 16384 < ffff88022767d900 3896864077 C Bi:8:005:2 0 416 = 4e434d48 0c003500 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff88022767d900 3896864129 S Bi:8:005:2 -115 16384 < ffff88022d639e40 3897644729 S Bo:8:005:1 -115 262 = 4e434d48 0c000f00 06010c00 49505300 10000000 b8004e00 00000000 00000000 ffff88022d639e40 3897644965 C Bo:8:005:1 0 262 > ffff88022b1de380 3897711770 C Bi:8:005:2 0 112 = 4e434d48 0c003600 70000c00 49505300 10000000 1c004e00 00000000 4500004e ffff88022b1de380 3897711812 S Bi:8:005:2 -115 16384 < ffff88022b07c600 3898646616 S Bo:8:005:1 -115 262 = 4e434d48 0c001000 06010c00 49505300 10000000 b8004e00 00000000 00000000 ffff88022b07c600 3898646848 C Bo:8:005:1 0 262 > ffff88022b1de200 3898697788 C Bi:8:005:2 0 112 = 4e434d48 0c003700 70000c00 49505300 10000000 1c004e00 00000000 4500004e ffff88022b1de200 3898697829 S Bi:8:005:2 -115 16384 < ffff88022b1de140 3901425927 C Bi:8:005:2 -104 0 driver with ZLP: ffff8802041d82c0 3651255294 C Bo:8:005:1 0 4096 > ffff88021a3ef380 3652103000 S Bo:8:005:1 -115 4096 = 4e434d48 0c003200 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff88021a3ef380 3652103315 C Bo:8:005:1 0 4096 > ffff8802041af540 3652439129 C Bi:8:005:2 0 416 = 4e434d48 0c002c00 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff8802041af540 3652439183 S Bi:8:005:2 -115 16384 < ffff8802041af240 3653099148 C Bi:8:005:2 0 416 = 4e434d48 0c002d00 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff8802041af240 3653099183 S Bi:8:005:2 -115 16384 < ffff88021a3efb00 3653101946 S Bo:8:005:1 -115 4096 = 4e434d48 0c003300 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff88021a3efb00 3653102201 C Bo:8:005:1 0 4096 > ffff8802041af9c0 3654039362 C Bi:8:005:2 0 416 = 4e434d48 0c002e00 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff8802041af9c0 3654039414 S Bi:8:005:2 -115 16384 < ffff88021a3ef980 3654101353 S Bo:8:005:1 -115 4096 = 4e434d48 0c003400 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff88021a3ef980 3654101622 C Bo:8:005:1 0 4096 > ffff88021a3efc80 3654999361 C Bi:8:005:2 0 416 = 4e434d48 0c002f00 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff88021a3efc80 3654999412 S Bi:8:005:2 -115 16384 < ffff88021a3ef200 3655102396 S Bo:8:005:1 -115 4096 = 4e434d48 0c003500 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff88021a3ef200 3655102737 C Bo:8:005:1 0 4096 > ffff88021a3efe00 3655949445 C Bi:8:005:2 0 416 = 4e434d48 0c003000 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff88021a3efe00 3655949491 S Bi:8:005:2 -115 16384 < ffff88021a3ef500 3656103498 S Bo:8:005:1 -115 4096 = 4e434d48 0c003600 00100c00 49505300 10000000 b8007a01 00000000 00000000 ffff88021a3ef500 3656103779 C Bo:8:005:1 0 4096 > ffff8802041af540 3657229210 C Bi:8:005:2 0 416 = 4e434d48 0c003100 a0010c00 49505300 10000000 1c007a01 00000000 4500017a ffff8802041af540 3657229251 S Bi:8:005:2 -115 16384 < ffff8802041af240 3659438084 C Bi:8:005:2 -104 0 ffff8802041af9c0 3659438159 C Bi:8:005:2 -104 0 ffff88021a3efc80 3659438206 C Bi:8:005:2 -104 0 Bjørn -- 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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