RE: [PATCH v3 4/4] vhost: stop using mempool for IOTLB cache

["Yuan, DukaiX" <dukaix.yuan@intel.com>]

Hi David,

I get an error message when I use qemu-6.2.0 to relaunch dpdk-l3fwd-power with Asan, I need your help to confirm this issue.
For more information please refer to https://bugs.dpdk.org/show_bug.cgi?id=1135.
Waiting for your reply.

Best regards,
Dukai,Yuan

> -----Original Message-----
> From: Maxime Coquelin <maxime.coquelin@redhat.com>
> Sent: 2022年7月26日 17:27
> To: David Marchand <david.marchand@redhat.com>; dev@dpdk.org
> Cc: Xia, Chenbo <Chenbo.Xia@intel.com>
> Subject: Re: [PATCH v3 4/4] vhost: stop using mempool for IOTLB cache
> 
> 
> 
> On 7/25/22 22:32, David Marchand wrote:
> > A mempool consumes 3 memzones (with the default ring mempool driver).
> > The default DPDK configuration allows RTE_MAX_MEMZONE (2560)
> memzones.
> >
> > Assuming there is no other memzones that means that we can have a
> > maximum of 853 mempools.
> >
> > In the vhost library, the IOTLB cache code so far was requesting a
> > mempool per vq, which means that at the maximum, the vhost library
> > could request mempools for 426 qps.
> >
> > This limit was recently reached on big systems with a lot of virtio
> > ports (and multiqueue in use).
> >
> > While the limit on mempool count could be something we fix at the DPDK
> > project level, there is no reason to use mempools for the IOTLB cache:
> > - the IOTLB cache entries do not need to be DMA-able and are only used
> >    by the current process (in multiprocess context),
> > - getting/putting objects from/in the mempool is always associated with
> >    some other locks, so some level of lock contention is already
> > present,
> >
> > We can convert to a malloc'd pool with objects put in a free list
> > protected by a spinlock.
> >
> > Signed-off-by: David Marchand <david.marchand@redhat.com>
> > ---
> >   lib/vhost/iotlb.c | 102 ++++++++++++++++++++++++++++------------------
> >   lib/vhost/iotlb.h |   1 +
> >   lib/vhost/vhost.c |   2 +-
> >   lib/vhost/vhost.h |   4 +-
> >   4 files changed, 67 insertions(+), 42 deletions(-)
> >
> 
> Thanks for working on this, this is definitely not needed to use mempool for
> this.
> 
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> 
> Maxime