From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shreyansh Jain Subject: Re: [PATCH 3/5] common/dpaax: add library for PA VA translation table Date: Thu, 11 Oct 2018 15:37:57 +0530 Message-ID: <16940ff0-278c-2376-1a86-6beaf0770a09@nxp.com> References: <20180925125423.7505-1-shreyansh.jain@nxp.com> <20180925125423.7505-4-shreyansh.jain@nxp.com> <894130a9-017c-348d-31f8-c4c23f517f25@nxp.com> <2d2e9008-fb5b-3ecd-2d2c-e86250f5d363@nxp.com> <5e153c76-6eaa-e6a5-28ed-7cec191d4581@intel.com> <2c377b57-c418-5c03-a23d-5da91ef898d0@nxp.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Cc: ferruh.yigit@intel.com, dev@dpdk.org To: "Burakov, Anatoly" Return-path: Received: from EUR03-AM5-obe.outbound.protection.outlook.com (mail-eopbgr30041.outbound.protection.outlook.com [40.107.3.41]) by dpdk.org (Postfix) with ESMTP id 8E2921B202 for ; Thu, 11 Oct 2018 12:08:25 +0200 (CEST) In-Reply-To: <2c377b57-c418-5c03-a23d-5da91ef898d0@nxp.com> Content-Language: en-US List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org Sender: "dev" On Thursday 11 October 2018 03:32 PM, Shreyansh Jain wrote: > On Thursday 11 October 2018 02:33 PM, Burakov, Anatoly wrote: >> On 09-Oct-18 11:45 AM, Shreyansh Jain wrote: >>> On Tuesday 25 September 2018 07:09 PM, Shreyansh Jain wrote: >>>> Hello Anatoly, >>>> >>>> On Tuesday 25 September 2018 06:58 PM, Burakov, Anatoly wrote: >>>>> On 25-Sep-18 1:54 PM, Shreyansh Jain wrote: >>>>>> A common library, valid for dpaaX drivers, which is used to maintain >>>>>> a local copy of PA->VA translations. >>>>>> >>>>>> In case of physical addressing mode (one of the option for FSLMC, and >>>>>> only option for DPAA bus), the addresses of descriptors Rx'd are >>>>>> physical. These need to be converted into equivalent VA for rte_mbuf >>>>>> and other similar calls. >>>>>> >>>>>> Using the rte_mem_virt2iova or rte_mem_virt2phy is expensive. This >>>>>> library is an attempt to reduce the overall cost associated with >>>>>> this translation. >>>>>> >>>>>> A small table is maintained, containing continuous entries >>>>>> representing a continguous physical range. Each of these entries >>>>>> stores the equivalent VA, which is fed during mempool creation, or >>>>>> memory allocation/deallocation callbacks. >>>>>> >>> >>> [...] >>> >>>> >>>>> >>>>> Also, a couple of nitpicks below. >>>>> >>>>>>   cosnfig/common_base                            |   5 + >>>>>>   config/common_linuxapp                        |   5 + >>>>>>   drivers/common/Makefile                       |   4 + >>>>>>   drivers/common/dpaax/Makefile                 |  31 ++ >>>>>>   drivers/common/dpaax/dpaax_iova_table.c       | 509 >>>>>> ++++++++++++++++++ >>>>>>   drivers/common/dpaax/dpaax_iova_table.h       | 104 ++++ >>>>>>   drivers/common/dpaax/dpaax_logs.h             |  39 ++ >>>>>>   drivers/common/dpaax/meson.build              |  12 + >>>>> >>>>> >>>>> >>>>>> +    DPAAX_DEBUG("Add: Found slot at (%"PRIu64")[(%zu)] for >>>>>> vaddr:(%p)," >>>>>> +            " phy(%"PRIu64"), len(%zu)", entry[i].start, e_offset, >>>>>> +            vaddr, paddr, length); >>>>>> +    return 0; >>>>>> +} >>>>>> + >>>>>> +int >>>>>> +dpaax_iova_table_del(phys_addr_t paddr, size_t len __rte_unused) >>>>> >>>>> len is not unused. >>>> >>>> I will fix this. >>>> Actually, this function itself is useless - more for symmetry reason. >>>> Callers would be either simply updating the table, or ignoring it >>>> completely. But, yes, this is indeed wrong that I set that unused. >>>> >>> >>> Actually, I was wrong in my first reply. In case of >>> dpaax_iova_table_del(), len is indeed redundant. This is because the >>> mapping is for a complete page (min of 2MB size), even if the request >>> is for lesser length. So, removal of a single entry (of fixed size) >>> would be done. >>> >>> In fact, while on this, I think deleting a PA->VA entry itself is >>> incorrect (not just useless). A single entry (~2MB equivalent) can >>> represent multiple users (working on a rte_malloc'd area, for >>> example). So, effectively, its always an update - not an add or del. >> >> I'm not sure what you mean here. If you got a mem event about memory >> area being freed, it's guaranteed to *not* have any users - neither >> malloc, nor any other memory. And len is always page-aligned. > > ok. Maybe I am getting this wrong, but consider this: > > 1) hugepage size=2MB > 2) a = malloc(1M) >   this will pin an entry in table for a block starting at VA=(a) and > PA=(a'). Each entry is of 2MB length - that means, even if someone were > to access a+1048577 for an equivalent PA, they would get it (though, > that is a incorrect access). > 3) b = malloc(1M) >   this *might* lead to a case where same 2MB page is used and > VA=(b==(a+1MB)). Being hugepage backed, PA=(b=PA(a)+1M). > = After b, the PA-VA table has a single entry of 2MB, representing two > mallocs. It can be used for translation for any thread requesting PAs of > a or b. > 4) Free(a) >  - this would attempt to remove one 2MB entry from PA-VA table. But, > 'b' is already valid. Access to get_pa(VA(b)) should return me the PA(b). >  - 'len' is not even used as the entry in PA-VA table is of a fixed size. Just to add to this: - if talking about the mem_event callback, it definitely won't be a case where same page is still being served under another rte_malloc - But, calls can come to delete from users of PA-VA table based on their own rte_free(). And, your comment makes me think - I should probably del entry from the table only when mem_event callback is received. > > In the above, (3) is an assumption I am making based on my understanding > how mem allocator is working. Is that wrong? > > Basically, this is a restriction of this table - it has a min chunk of > 2MB - even for 1G hugepages - and hence, it is not possible to honor > deletes. I know this is convoluted logic - but, this keeps it simple and > use-able without much performance impact. > > [...] >