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From: Greg Kurz <groug@kaod.org>
To: qemu-devel@nongnu.org
Cc: Stefan Hajnoczi <stefanha@redhat.com>,
	"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
	Maxime Coquelin <maxime.coquelin@redhat.com>,
	Laurent Vivier <lvivier@redhat.com>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Yajun Wu <yajunw@nvidia.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	Parav Pandit <parav@nvidia.com>,
	qemu-stable@nongnu.org, Greg Kurz <groug@kaod.org>
Subject: [PATCH 0/2] vhost-user: Remove the nested event loop to unbreak the DPDK use case
Date: Thu, 19 Jan 2023 18:24:22 +0100	[thread overview]
Message-ID: <20230119172424.478268-1-groug@kaod.org> (raw)

The nested event loop was introduced in QEMU 6.0 to allow servicing
of requests coming from the slave channel while waiting for an ack
from the back-end on the master socket. It turns out this is fragile
and breaks if the servicing of the slave channel causes a new message
to be sent on the master socket. This is exactly what happens when
using DPDK as reported in [0].

The only identified user for the nested loop is DAX enablement that
isn't upstream yet. Just drop the code for now. Some more clever
solution should be designed when the need to service concurrent
requests from both channels arises again.

Greg Kurz (2):
  Revert "vhost-user: Monitor slave channel in vhost_user_read()"
  Revert "vhost-user: Introduce nested event loop in vhost_user_read()"

 hw/virtio/vhost-user.c | 100 ++++-------------------------------------
 1 file changed, 8 insertions(+), 92 deletions(-)

-- 
2.39.0




             reply	other threads:[~2023-01-20 14:01 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-19 17:24 Greg Kurz [this message]
2023-01-19 17:24 ` [PATCH 1/2] Revert "vhost-user: Monitor slave channel in vhost_user_read()" Greg Kurz
2023-01-19 18:39   ` Greg Kurz
2023-01-19 21:10   ` Stefan Hajnoczi
2023-01-20 15:03   ` Maxime Coquelin
2023-01-19 17:24 ` [PATCH 2/2] Revert "vhost-user: Introduce nested event loop " Greg Kurz
2023-01-20 15:13   ` Maxime Coquelin
2023-01-23  8:21 ` [PATCH 0/2] vhost-user: Remove the nested event loop to unbreak the DPDK use case Greg Kurz

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