From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-it0-x244.google.com (mail-it0-x244.google.com. [2607:f8b0:4001:c0b::244]) by gmr-mx.google.com with ESMTPS id y128si698900ywa.6.2017.10.11.11.03.07 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 11 Oct 2017 11:03:07 -0700 (PDT) Received: by mail-it0-x244.google.com with SMTP id y15so4084953ita.4 for ; Wed, 11 Oct 2017 11:03:07 -0700 (PDT) Return-Path: Subject: Re: Is the Scratchpad Implementation Using a LUT Standard? References: <9aa73260-8b02-4e86-b7d4-9bc3afd745a6@googlegroups.com> <000001d341d2$87574f20$9605ed60$@dell.com> <6107eb07-3889-4f1a-ad50-264256772dae@googlegroups.com> <38ffd174-b66f-4077-8cdc-679e412242fc@googlegroups.com> <20171011174114.GA25306@mobilestation> From: Logan Gunthorpe Message-ID: Date: Wed, 11 Oct 2017 12:03:04 -0600 MIME-Version: 1.0 In-Reply-To: <20171011174114.GA25306@mobilestation> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US To: Serge Semin Cc: linux-ntb List-ID: On 11/10/17 11:41 AM, Serge Semin wrote: > You are mistaken. IDT PCIe switch have LUT. There are 24 of them available at > the current hardware for each NTB. All of them are available to be used over > IDT NTB driver as well as all MWs with direct address translation. > Additionally It is true to say about just one LUT entry usage per peer, only if > you got just two NTB-ports available per device. What if you got eight or even more > of them? In this case you'd need to have as many LUT entries reserved as there are > peers available to have connections to. In this case reservation doesn't seem so > inexpensive. As far as I can see from the switchtec brief documents, there can be > up to 48 NTBs per device. So in this case we'd loose 48 MWs just to have some > stupid scratchpads, which is, according to your words, a third part of all the LUT > MWs available to a port. Ah, fair, I wasn't aware the IDT had LUT support. Using up a third of the LUT windows does not seem like a problem at all considering we have no other use for them. Note: the switchtec code also used the shared_mw for link management, not just providing scratchpads. But once the upper layers are reworked to not require scratchpads I'd be fine with removing them from the shared_mw. Logan