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From: Markus Armbruster <armbru@redhat.com>
To: Yuri Benditovich <yuri.benditovich@daynix.com>
Cc: "Andrew Melnichenko" <andrew@daynix.com>,
	"Daniel P. Berrangé" <berrange@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Jason Wang" <jasowang@redhat.com>,
	qemu-devel@nongnu.org, "Yan Vugenfirer" <yan@daynix.com>,
	"Eric Blake" <eblake@redhat.com>
Subject: Re: [PATCH 5/5] qmp: Added qemu-ebpf-rss-path command.
Date: Mon, 30 Aug 2021 08:10:28 +0200	[thread overview]
Message-ID: <87v93n8nu3.fsf@dusky.pond.sub.org> (raw)
In-Reply-To: <CAOEp5OcyvQ9Y2onyHuJnwjtWK+Tx9QxYXUePd1kJ=V9+H9wraw@mail.gmail.com> (Yuri Benditovich's message of "Sun, 29 Aug 2021 23:13:42 +0300")

Yuri Benditovich <yuri.benditovich@daynix.com> writes:

> On Tue, Aug 24, 2021 at 9:41 AM Markus Armbruster <armbru@redhat.com> wrote:
>>
>> Andrew Melnichenko <andrew@daynix.com> writes:
>>
>> > Hi,
>> >
>> >> The helper may or may not be installed at the path compiled into QEMU.
>> >>
>> > Yes, so the helper will not be called - QEMU will try to initiate eBPF RSS
>> > or use "in-qemu" RSS.
>>
>> My point is: the proposed command's mission is to help the management
>> application run the right helper.  However, its advice is *unreliable*.
>> It may point to the wrong helper, or to nothing at all.  The right
>> helper may still exist elsewhere.
>
> Hi Markus,
> Indeed the intention of this command is to return the proper helper.
> Especially in the case of RSS helper this is *reliable* advice and it
> points to the helper that was built together with QEMU, i.e. with the
> same headers.
> This was discussed earlier, for example in
> https://lists.nongnu.org/archive/html/qemu-devel/2021-06/msg02248.html
>
>>
>> I suspect you're trying to address the problem at the wrong level.
>
> What is the proper solution for the problem from your point of view?

I'll explain in more detail, but first I'd like you to answer my
question below.

>> Similar versioning issues exist with other helpers.  We've been doing
>> fine without QEMU providing unreliable advice on where they might sit in
>> the file system.  What makes this one different?
>
> This one is required to be *fully synchronized* with the existing build of QEMU.
> Other helpers are probably less restrictive and do not have common
> structures definitions with the QEMU, otherwise they would face the
> same problem.
>
>>
>> >> What happens when you use the wrong helper?
>
> Our intention is that libvirt should never use the wrong RSS helper.
> But it does not have any ability to check which helper is compatible
> with the QEMU.
> QEMU can easily recognize the correct one.

You did not actually answer my question :)

So let's try again: if libvirt does use the wrong RSS helper, how does
the system behave?

>> >>
>> > UB - in most cases, eBPF program will work with wrong configurations.
>> > That's why the stamp was added.
>> >
>> > query-helper-paths checks the stamp only for RSS helper.
>>
>> I have no idea what you're talking about :)
>>
>> My best guess is that you're trying to tell me that attempting to work
>> with the wrong helper will fail cleanly due to some stamp check.  That
>> would be nice.
>>



  reply	other threads:[~2021-08-30  6:11 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-13 15:37 [PATCH 0/5] ebpf: Added ebpf helper for libvirtd Andrew Melnychenko
2021-07-13 15:37 ` [PATCH 1/5] ebpf: Added eBPF initialization by fds and map update Andrew Melnychenko
2021-08-20  3:34   ` Jason Wang
2021-08-25 18:13     ` Andrew Melnichenko
2021-07-13 15:37 ` [PATCH 2/5] virtio-net: Added property to load eBPF RSS with fds Andrew Melnychenko
2021-08-20  3:36   ` Jason Wang
2021-08-25 18:18     ` Andrew Melnichenko
2021-07-13 15:37 ` [PATCH 3/5] qmp: Added the helper stamp check Andrew Melnychenko
2021-07-13 15:37 ` [PATCH 4/5] ebpf_rss_helper: Added helper for eBPF RSS Andrew Melnychenko
2021-08-20  3:40   ` Jason Wang
2021-08-25 18:24     ` Andrew Melnichenko
2021-09-01  6:37       ` Jason Wang
2021-08-30 17:07     ` Yuri Benditovich
2021-09-01  6:42       ` Jason Wang
2021-09-06 15:50         ` Andrew Melnichenko
2021-09-07  3:22           ` Jason Wang
2021-09-07 10:40         ` Yuri Benditovich
2021-09-08  3:45           ` Jason Wang
2021-09-09  0:00             ` Yuri Benditovich
2021-09-09  1:16               ` Jason Wang
2021-09-09 23:43                 ` Yuri Benditovich
2021-09-10  1:37                   ` Jason Wang
2021-07-13 15:37 ` [PATCH 5/5] qmp: Added qemu-ebpf-rss-path command Andrew Melnychenko
2021-08-07 12:54   ` Markus Armbruster
2021-08-10 11:58     ` Andrew Melnichenko
2021-08-24  6:41       ` Markus Armbruster
2021-08-25 18:45         ` Andrew Melnichenko
2021-08-26  4:53           ` Markus Armbruster
2021-08-29 20:13         ` Yuri Benditovich
2021-08-30  6:10           ` Markus Armbruster [this message]
2021-08-30  7:51             ` Yuri Benditovich
2021-08-30  8:13               ` Markus Armbruster
2021-08-30 16:56                 ` Yuri Benditovich
2021-08-31 15:00                   ` Markus Armbruster
2021-08-31 19:37                     ` Andrew Melnichenko
2021-09-01  7:16                       ` Markus Armbruster
     [not found]                         ` <CABcq3pGzs=RqLCuu70KyWt7W6T=qEhihK6v=iHJyfuGqiN_Q+A@mail.gmail.com>
     [not found]                           ` <CAOEp5Oc_uUn2nJq+B+SK-iQSo5udyUTirWHS5=8N0JxerRaz7A@mail.gmail.com>
2021-09-09 10:35                             ` Andrew Melnichenko
2021-09-02 16:06                   ` Markus Armbruster
2021-07-22  8:37 ` [PATCH 0/5] ebpf: Added ebpf helper for libvirtd Andrew Melnichenko
2021-08-16 11:57   ` Yuri Benditovich
2021-08-17  5:49     ` Jason Wang
2021-08-20  3:43 ` Jason Wang

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