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

[Maxime Coquelin <maxime.coquelin@redhat.com>]

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.

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