From: Sergio Gonzalez Monroy <sergio.gonzalez.monroy@intel.com>
To: "Tan, Jianfeng" <jianfeng.tan@intel.com>,
Stephen Hemminger <stephen@networkplumber.org>,
"dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary process
Date: Wed, 12 Jul 2017 08:31:40 +0100 [thread overview]
Message-ID: <b3447521-4ee8-ad40-8908-4a34d3bc6814@intel.com> (raw)
In-Reply-To: <ED26CBA2FAD1BF48A8719AEF02201E3651230A08@SHSMSX103.ccr.corp.intel.com>
On 12/07/2017 03:45, Tan, Jianfeng wrote:
>
>> -----Original Message-----
>> From: Gonzalez Monroy, Sergio
>> Sent: Tuesday, July 11, 2017 7:36 PM
>> To: Tan, Jianfeng; Stephen Hemminger; dev@dpdk.org
>> Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary
>> process
>>
>> On 11/07/2017 02:56, Tan, Jianfeng wrote:
>>>> -----Original Message-----
>>>> From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Stephen
>>>> Hemminger
>>>> Sent: Tuesday, July 11, 2017 9:13 AM
>>>> To: dev@dpdk.org
>>>> Cc: Stephen Hemminger
>>>> Subject: [dpdk-dev] [RFC] pci: force address of mappings in secondary
>>>> process
>>>>
>>>> The PCI memory resources in the secondary process should be in
>>>> the exact same location as the primary process. Otherwise
>>>> there is a risk of a stray pointer.
>>>>
>>>> Not sure if this is right, but it looks like a potential
>>>> problem.
>>>>
>>>> ---
>>>> lib/librte_eal/common/eal_common_pci_uio.c | 2 +-
>>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>>>
>>>> diff --git a/lib/librte_eal/common/eal_common_pci_uio.c
>>>> b/lib/librte_eal/common/eal_common_pci_uio.c
>>>> index 367a6816dcb8..2156b1a436c4 100644
>>>> --- a/lib/librte_eal/common/eal_common_pci_uio.c
>>>> +++ b/lib/librte_eal/common/eal_common_pci_uio.c
>>>> @@ -77,7 +77,7 @@ pci_uio_map_secondary(struct rte_pci_device *dev)
>>>>
>>>> void *mapaddr = pci_map_resource(uio_res-
>>>>> maps[i].addr,
>>>> fd, (off_t)uio_res->maps[i].offset,
>>>> - (size_t)uio_res->maps[i].size, 0);
>>>> + (size_t)uio_res->maps[i].size,
>>>> MAP_FIXED);
>>>> /* fd is not needed in slave process, close it */
>>>> close(fd);
>>>> if (mapaddr != uio_res->maps[i].addr) {
>>>> --
>>>> 2.11.0
>>> +1 for this RFC. I also once encounter such problem, and I use the same
>> way to solve it. The addr parameter of mmap() syscall is only a hint instead of
>> a must even the VMA is not occupied yet.
>>> Thanks,
>>> Jianfeng
>> How do you know the VMA is not occupied?
> I did by check /proc/self/maps.
>
>> I think the risk here is that the dynamic linker loaded some shared
>> library in that VMA, and forcing MAP_FIXED is not a safe solution.
>> What I have observed is that Linux will return a different VMA than the
>> one hinted when there is already a mapping in the requested/hinted VMA.
> IMO, that's not the target of this RFC. The target is to solve the situation (in current primary/secondary model) that kernel will not use the addr even there's no VMA on that addr. This is my understanding, Stephen, please correct me if I'm wrong.
The point I was trying to make is, that you do not know if there is a
mapping or not in that address, and by using MAP_FIXED it will unmap
whatever was in there before.
So unless you parse /proc/self/maps and check that the VMA range is not
being used, forcing MAP_FIXED is not safe.
>> I reckon this is a similar issue as we have with the multi-process model
>> when we do not get the VMA requested for the huge-pages.
>> AFAIK we do not have a robust solution for this issue other than restart
>> the program and hope the dynamic linker does not map anything in the VMA
>> ranges that we need to map from the primary. This is also assuming that
>> the application does not allocate memory and maps things before calling
>> eal_init as it could potentially use VMA ranges that we need in the
>> secondary process.
> This is another problem.
It is the same problem, VMA ranges that we need to map being already used.
Thanks,
Sergio
>> The proposal for new secondary process model would solve these issues:
>> http://dpdk.org/ml/archives/dev/2017-May/066147.html
> And yes, this might happen to solve the targeted issue in this RFC. But before the new model is out, this patch seems a workable way for the original issue.
>
> Thanks,
> Jianfeng
>
>> Thanks,
>> Sergio
next prev parent reply other threads:[~2017-07-12 7:31 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-11 1:12 Stephen Hemminger
2017-07-11 1:56 ` Tan, Jianfeng
2017-07-11 11:35 ` Sergio Gonzalez Monroy
2017-07-11 20:00 ` Stephen Hemminger
2017-07-12 7:24 ` Sergio Gonzalez Monroy
2017-07-12 2:45 ` Tan, Jianfeng
2017-07-12 7:31 ` Sergio Gonzalez Monroy [this message]
2017-07-12 8:58 ` Tan, Jianfeng
2019-01-23 19:21 ` Ferruh Yigit
2019-01-23 20:37 ` Stephen Hemminger
2019-01-28 9:59 ` Burakov, Anatoly
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