linux-kernel - Re: EEVDF/vhost regression (bisected to 86bfbb7ce4f6 sched/fair: Add lag based placement)

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Date: Tue, 19 Mar 2024 09:59:30 +0100
From: Tobias Huschle <huschle@...ux.ibm.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: Luis Machado <luis.machado@....com>, Jason Wang <jasowang@...hat.com>,
        Abel Wu <wuyun.abel@...edance.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        virtualization@...ts.linux.dev, netdev@...r.kernel.org,
        nd <nd@....com>
Subject: Re: EEVDF/vhost regression (bisected to 86bfbb7ce4f6 sched/fair: Add
 lag based placement)

On 2024-03-19 09:29, Michael S. Tsirkin wrote:
> On Tue, Mar 19, 2024 at 09:21:06AM +0100, Tobias Huschle wrote:
>> On 2024-03-15 11:31, Michael S. Tsirkin wrote:
>> > On Fri, Mar 15, 2024 at 09:33:49AM +0100, Tobias Huschle wrote:
>> > > On Thu, Mar 14, 2024 at 11:09:25AM -0400, Michael S. Tsirkin wrote:
>> > > >
>> >
>> > Could you remind me pls, what is the kworker doing specifically that
>> > vhost is relying on?
>> 
>> The kworker is handling the actual data moving in memory if I'm not
>> mistaking.
> 
> I think that is the vhost process itself. Maybe you mean the
> guest thread versus the vhost thread then?

My understanding was that vhost writes data into a file descriptor which 
then triggers eventfd.

That's at least how I read the vhost code if I remember correctly.

The handler beneath (the kworker) then runs the actual instructions that 
move the data to the receiving vhost on the other end of the connection.

Again, I might be wrong here.