Re: [dpdk-dev] [PATCH v2] net/virtio: fix AVX512 datapath selection

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: Tuesday, May 12, 2020 4:36 PM
> To: Liu, Yong <yong.liu@intel.com>; Yigit, Ferruh <ferruh.yigit@intel.com>
> Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; David
> Marchand <david.marchand@redhat.com>; Richardson, Bruce
> <bruce.richardson@intel.com>; Nicolau, Radu <radu.nicolau@intel.com>;
> Luca Boccassi <bluca@debian.org>; Wang, Zhihong
> <zhihong.wang@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>
> Subject: Re: [PATCH v2] net/virtio: fix AVX512 datapath selection
> 
> 
> 
> On 5/12/20 5:29 AM, Liu, Yong wrote:
> >
> >
> >> -----Original Message-----
> >> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> Sent: Tuesday, May 12, 2020 3:50 AM
> >> To: Yigit, Ferruh <ferruh.yigit@intel.com>; Wang, Zhihong
> >> <zhihong.wang@intel.com>; Ye, Xiaolong <xiaolong.ye@intel.com>; Liu,
> >> Yong <yong.liu@intel.com>
> >> Cc: dev@dpdk.org; Thomas Monjalon <thomas@monjalon.net>; David
> >> Marchand <david.marchand@redhat.com>; Richardson, Bruce
> >> <bruce.richardson@intel.com>; Nicolau, Radu <radu.nicolau@intel.com>;
> >> Luca Boccassi <bluca@debian.org>
> >> Subject: Re: [PATCH v2] net/virtio: fix AVX512 datapath selection
> >>
> >>
> >>
> >> On 5/11/20 8:48 PM, Ferruh Yigit wrote:
> >>> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> >>>
> >>> The AVX512 packed ring datapath selection was only done
> >>> at build time, but it should also be checked at runtime
> >>> that the CPU supports it.
> >>>
> >>> This patch add a CPU flags check so that non-vectorized
> >>> path is selected at runtime if AVX512 is not supported.
> >>>
> >>> Also in meson build enable vectorization only for relevant file, not for
> >>> all driver.
> >>>
> >>> Fixes: ccb10995c2ad ("net/virtio: add election for vectorized path")
> >>>
> >>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >>> Signed-off-by: Ferruh Yigit <ferruh.yigit@intel.com>
> >>> ---
> >>> Cc: Bruce Richardson <bruce.richardson@intel.com>
> >>> Cc: Radu Nicolau <radu.nicolau@intel.com>
> >>> Cc: Luca Boccassi <bluca@debian.org>
> >>>
> >>> For meson I mainly adapted implementation from other driver, not
> able
> >> to
> >>> test or verify myself.
> >>> ---
> >>>  drivers/net/virtio/meson.build     | 9 +++++++--
> >>>  drivers/net/virtio/virtio_ethdev.c | 6 ++++--
> >>>  2 files changed, 11 insertions(+), 4 deletions(-)
> >>
> >> Thanks Ferruh, I cannot test either right now but it looks good to me:
> >>
> >
> > Hi Maxime & Ferruh,
> > IMHO, meson build update is the essential part for fixing unexpected
> AVX512 instructions.
> > Change in virtio_ethdev may cause building issues on ppc and arm
> platform.  Is it convenient to revert that change?
> 
> As replied to v1:
> 
> With a bit more of context, we can see that it only affects packed ring
> when CC_AVX512_SUPPORT is set. So it does break neither split ring nor
> ARM/PPC:
> 
> 	if (vectorized) {
> 		if (!vtpci_packed_queue(hw)) {
> 			hw->use_vec_rx = 1;
> 		} else {
> #if !defined(CC_AVX512_SUPPORT)
> 			PMD_DRV_LOG(INFO,
> 				"building environment do not support
> packed ring vectorized");
> #else
> 			if
> (rte_cpu_get_flag_enabled(RTE_CPUFLAG_AVX512F)) {
> 				hw->use_vec_rx = 1;
> 				hw->use_vec_tx = 1;
> 			}
> #endif
> 		}
> 	}
> 
> So IMO, no revert has to be done.
> 

Ok, I messed it with my previous building fix.  It will be no harm for  this double check. 

> > Regards,
> > Marvin
> >
> >> In case you're waiting for it:
> >> Acked-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >>
> >> Maxime
> >