Re: [dpdk-stable] [dpdk-dev] [PATCH] vhost: make iotlb cache name unique among multi processes

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 3/10/20 1:44 PM, Van Haaren, Harry wrote:
>> -----Original Message-----
>> From: dev <dev-bounces@dpdk.org> On Behalf Of Ye Xiaolong
>> Sent: Tuesday, March 10, 2020 11:32 AM
>> To: Itsuro Oda <oda@valinux.co.jp>
>> Cc: dev@dpdk.org; maxime.coquelin@redhat.com; Wang, Zhihong
>> <zhihong.wang@intel.com>; stable@dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH] vhost: make iotlb cache name unique among
>> multi processes
>>
>> On 03/10, Itsuro Oda wrote:
>>> Currently, iotlb cache name is comprised of vid and virtqueue
>>> index. For example, "iotlb_cache_0_0". Because vid is assigned
>>> per process, iotlb cache name is not unique among multi processes.
>>> For example a secondary process uses a vhost
>>> (ex. eth_vhost0,iface=/tmp/sock0) and another secondary process
>>> uses a vhost (ex. eth_vhost1,iface=/tmp/sock1), iotlb cache
>>> name of both vhost ("iotlb_cache_0_0") are same and as a result
>>> iotlb cache is broken.
>>>
>>> This patch makes iotlb cache name unique among milti processes
>>> by using the interface name not vid to comprise iotlb cache name.
>>> Since the length of interface name is variable, this patch uses
>>> hash value calculated by the interface name.
>>>
>>> Fixes: d012d1f293f4 (vhost: add IOTLB helper functions)
>>> Cc: stable@dpdk.org
>>>
>>> Signed-off-by: Itsuro Oda <oda@valinux.co.jp>
>>> ---
>>> lib/librte_vhost/iotlb.c | 8 ++++++--
>>> 1 file changed, 6 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/lib/librte_vhost/iotlb.c b/lib/librte_vhost/iotlb.c
>>> index bc1758528..0992c145b 100644
>>> --- a/lib/librte_vhost/iotlb.c
>>> +++ b/lib/librte_vhost/iotlb.c
>>> @@ -6,6 +6,7 @@
>>> #include <numaif.h>
>>> #endif
>>>
>>> +#include <rte_jhash.h>
>>> #include <rte_tailq.h>
>>>
>>> #include "iotlb.h"
>>> @@ -288,6 +289,7 @@ vhost_user_iotlb_init(struct virtio_net *dev, int
>> vq_index)
>>> 	char pool_name[RTE_MEMPOOL_NAMESIZE];
>>> 	struct vhost_virtqueue *vq = dev->virtqueue[vq_index];
>>> 	int socket = 0;
>>> +	uint32_t val;
>>>
>>> 	if (vq->iotlb_pool) {
>>> 		/*
>>> @@ -308,8 +310,10 @@ vhost_user_iotlb_init(struct virtio_net *dev, int
>> vq_index)
>>> 	TAILQ_INIT(&vq->iotlb_list);
>>> 	TAILQ_INIT(&vq->iotlb_pending_list);
>>>
>>> -	snprintf(pool_name, sizeof(pool_name), "iotlb_cache_%d_%d",
>>> -			dev->vid, vq_index);
>>> +	val = rte_jhash(dev->ifname, strlen(dev->ifname), 0);
>>> +	snprintf(pool_name, sizeof(pool_name), "iotlb_cache_%08x_%d",
>>> +			val, vq_index);
>>> +	VHOST_LOG_CONFIG(DEBUG, "IOTLB cache name: %s\n", pool_name);
> 
> Although very unlikely, what would happen if there is a hash-collision?
> 
> For example imagine two different names hash to the same "val", from
> my understanding they will now use the same IOTLB but should not share one.
> 
> <snip>
> 

+1.

Instead of a hash, maybe use the process ID:
snprintf(pool_name, sizeof(pool_name), "iotlb_cache_%u_%d_%d",
	 pid, dev->vid, vq_index);