On 2022-06-02 10:26, Li Zhang wrote:
Hi Pai,
Thanks a lot. It helps.
These patches allow ovs to decide to disable or enable AVX512 if I
understand it correctly.
Is it recommended to enable AVX512? AVX512 is enabled by default.
It is disabled in DPDK because it is experimental. I wonder if I
should disable it, it may cause performance worse.
Look at https://en.wikipedia.org/wiki/AVX-512
AVX512 is CPU model dependent. Code will break if the instructions are
run on a cpu without them. Which is why they are typically not-compiled
in. Each environment will need to make that decision explicit. If your
environment supports the instructions, then I'd probably compile in for
OVS & DPRK. If you need code to transport all over the place, then best
to disable them.
Thanks
Li
On Thu, Jun 2, 2022 at 4:00 PM Pai G, Sunil <sunil.pa...@intel.com> wrote:
Hi Li,
The assumption of ovs being dependent on dpdk for avx512 might not be true.
I found these two commits below in ovs-2.14.2 which strips out the "-march" and
"-mno-avx512f" flags exported by dpdk i.e removes dependency on DPDK. The reason for this
is rightly mentioned below as well. Hope this helps.
commit bb8f0e2a810889241f1d886d160ccee9b96c4d63
Author: Ian Stokes <ian.sto...@intel.com>
Date: Fri Jan 15 15:46:02 2021 +0000
acinclude: Strip out -mno-avx512f provided by DPDK.
DPDK forces '-mno-avx512f' flag for the application if the toolchain
used to build DPDK had broken AVX512 support.
DPDK forces '-mno-avx512f' flag for the application if the toolchain
used to build DPDK had broken AVX512 support. But OVS could be built
with a completely different or fixed toolchain with correct avx512
support.
Fix that by stripping out `-mno-avx512f` as we already do for '-march'.
This will allow the OVS to decide if the AVX512 can be used.
Reordering of CFLAGS (i.e. adding DPDK flags before OVS ones) is not an
option since autotools might reorder them back later and it's very
unpredictable.
Reported-at: https://github.com/openvswitch/ovs-issues/issues/201
Signed-off-by: Ilya Maximets <i.maxim...@ovn.org>
Co-authored-by: Ilya Maximets <i.maxim...@ovn.org>
Signed-off-by: Ian Stokes <ian.sto...@intel.com>
commit e9f9104d00006a83ce7efd702120171835991779
Author: Ian Stokes <ian.sto...@intel.com>
Date: Fri Jan 15 14:54:04 2021 +0000
acinclude: Strip out -march provided by DPDK.
DPDK flags may include -march. Forcing -march could be
considered too heavy a requirement when users compile OVS from
source and could override user provided options.
Resolve this by stripping -march from provided DPDK flags.
Signed-off-by: Ian Stokes <ian.sto...@intel.com>
Thanks and Regards,
Sunil
-----Original Message-----
From: discuss <ovs-discuss-boun...@openvswitch.org> On Behalf Of Li Zhang
Sent: Thursday, June 2, 2022 6:35 PM
To: ovs-discuss@openvswitch.org
Subject: [ovs-discuss] One question about AVX512 support
Hi all,
We are using openvswitch 2.14.2, and dpdk-19.11.4. I found avx512 is
enabled by default but it's disabled in DPDK. But I think ovs is dependent
on the dpdk library, right? But why does ovs work with
avx512 disabled in DPDK?
I am not quite sure about the relationship between OVS and DPDK, any
suggestions?
--
Best Regards
-Li
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