netdev - RE: [PATCH net-next v2 2/3] r8152: cleartheflagofSCHEDULE

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Message-ID: <0835B3720019904CB8F7AA43166CEEB2ECE0DF@RTITMBSV03.realtek.com.tw>
Date:	Mon, 10 Nov 2014 05:23:14 +0000
From:	Hayes Wang <hayeswang@...ltek.com>
To:	Francois Romieu <romieu@...zoreil.com>
CC:	David Miller <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	nic_swsd <nic_swsd@...ltek.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [PATCH net-next v2 2/3] r8152: cleartheflagofSCHEDULE_TASKLETintasklet

 Francois Romieu [mailto:romieu@...zoreil.com] 
> Sent: Sunday, November 09, 2014 6:12 AM
[...]
> The performance explanation leaves me a bit unconvinced. Without any
> figure one could simply go for the always locked clear_bit because of:
> 1. the "I'm racy" message that the open-coded test + set sends
> 2. the extra work needed to avoid 1 (comment, explain, ...).

Thanks. I would modify this patch with clear_bit only.

> The extra time could thus be used to see what happens when napi is
> shoehorned in this tasklet machinery. I'd naively expect it to be
> relevant for efficiency.

I thought about NAPI, but I gave up. The reasons are
1. I don't sure if it would run when autosuspending.
2. There is no hw interrupt for USB device. And I have
   no idea about how to check if the USB transfer is
   completed by polling.
3. I have to control the rx packets numbers in poll().
   However, I couldn't control the packets number for
   each bulk-in transfer. I have to do extra works to
   deal with the rx flow.
4. I don't find much different between tasklet and NAPI.

Best Regards,
Hayes
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