From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f171.google.com (mail-pd0-f171.google.com [209.85.192.171]) by kanga.kvack.org (Postfix) with ESMTP id 860E26B0035 for ; Thu, 29 May 2014 19:44:49 -0400 (EDT) Received: by mail-pd0-f171.google.com with SMTP id y13so279986pdi.30 for ; Thu, 29 May 2014 16:44:49 -0700 (PDT) Received: from lgemrelse7q.lge.com (LGEMRELSE7Q.lge.com. [156.147.1.151]) by mx.google.com with ESMTP id cs2si2896429pbc.242.2014.05.29.16.44.47 for ; Thu, 29 May 2014 16:44:48 -0700 (PDT) Date: Fri, 30 May 2014 08:45:22 +0900 From: Minchan Kim Subject: Re: virtio ring cleanups, which save stack on older gcc Message-ID: <20140529234522.GL10092@bbox> References: <87oayh6s3s.fsf@rustcorp.com.au> <1401348405-18614-1-git-send-email-rusty@rustcorp.com.au> <20140529074117.GI10092@bbox> <87fvjs7sge.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87fvjs7sge.fsf@rustcorp.com.au> Sender: owner-linux-mm@kvack.org List-ID: To: Rusty Russell Cc: Linus Torvalds , Dave Chinner , Jens Axboe , Linux Kernel Mailing List , Andrew Morton , linux-mm , "H. Peter Anvin" , Ingo Molnar , Peter Zijlstra , Mel Gorman , Rik van Riel , Johannes Weiner , Hugh Dickins , "Michael S. Tsirkin" , Dave Hansen , Steven Rostedt On Thu, May 29, 2014 at 08:38:33PM +0930, Rusty Russell wrote: > Minchan Kim writes: > > Hello Rusty, > > > > On Thu, May 29, 2014 at 04:56:41PM +0930, Rusty Russell wrote: > >> They don't make much difference: the easier fix is use gcc 4.8 > >> which drops stack required across virtio block's virtio_queue_rq > >> down to that kmalloc in virtio_ring from 528 to 392 bytes. > >> > >> Still, these (*lightly tested*) patches reduce to 432 bytes, > >> even for gcc 4.6.4. Posted here FYI. > > > > I am testing with below which was hack for Dave's idea so don't have > > a machine to test your patches until tomorrow. > > So, I will queue your patches into testing machine tomorrow morning. > > More interesting would be updating your compiler to 4.8, I think. > Saving <100 bytes on virtio is not going to save you, right? But in my report, virtio_ring consumes more than yours. As I mentioned other thread to Steven, I don't know why stacktrace report vring_add_indirect consumes 376-byte. Apparently, objdump says it didn't consume too much so I'd like to test your patches and see the result. Thanks. [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 10) 6376 376 vring_add_indirect+0x36/0x200 [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 11) 6000 144 virtqueue_add_sgs+0x2e2/0x320 [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 12) 5856 288 __virtblk_add_req+0xda/0x1b0 [ 1065.604404] kworker/-5766 0d..2 1071625993us : stack_trace_call: 13) 5568 96 virtio_queue_rq+0xd3/0x1d0 > > Cheers, > Rusty. > > -- > To unsubscribe, send a message with 'unsubscribe linux-mm' in > the body to majordomo@kvack.org. For more info on Linux MM, > see: http://www.linux-mm.org/ . > Don't email: email@kvack.org -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org