On Mon, Jun 13, 2016 at 10:06:22AM +0000, Tan, Jianfeng wrote:
>
>
> > -----Original Message-----
> > From: Yuanhan Liu [mailto:yuanhan.liu at linux.intel.com]
> > Sent: Monday, June 13, 2016 5:52 PM
> > To: Tan, Jianfeng
> > Cc: dev at dpdk.org; Xie, Huawei
> > Subject: Re: [dpdk-dev] [PATCH] virtio: fix allocating virtnet_rx not mem
> > aligned
> >
> > On Mon, Jun 13, 2016 at 05:21:01PM +0800, Yuanhan Liu wrote:
> > > On Sun, Jun 12, 2016 at 02:29:42PM +0000, Jianfeng Tan wrote:
> > > > Compile DPDK with clang, below line in virtio_rxtx.c could be
> > > > optimized with four "VMOVAPS ymm, m256".
> > > > memset(&rxvq->fake_mbuf, 0, sizeof(rxvq->fake_mbuf));
> > > >
> > > > This instruction requires memory address is 32-byte aligned.
> > > > Or, it leads to segfault.
> > >
> > > That looks like a dangerous optimization to me. If that's the case,
> > > doesn't it mean we have to make sure the address is always aligned
> > > properly while calling memset?
> >
> > Above is just a side note. Anyway, I think making sure vq is cache
> > aligned is good here. So, I will apply it. BTW, do you mind if I
> > squash your 2 fixes into Huawei's Rx/Tx split commit? His commit is
> > not pushed to upstream yet, therefore I can still do rebase: I'm
> > thinking it's better to have one working commit other than one broken
> > commit followed with several fixing commits. And of course, I will
> > mention your contribution in the commit log.
>
> Not a problem from my side. But Huawei seems to have concerns on this fix.
> You can do that for the other fix firstly.
What's the concern? Despite the clang issue (I still have no idea why
clang would go that aggressively), I think making vq cache aligned is
generically a good idea.
--yliu
