From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 4D44BC07E9B for ; Wed, 21 Jul 2021 09:37:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 348B661181 for ; Wed, 21 Jul 2021 09:37:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237202AbhGUIzu convert rfc822-to-8bit (ORCPT ); Wed, 21 Jul 2021 04:55:50 -0400 Received: from szxga02-in.huawei.com ([45.249.212.188]:7409 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237393AbhGUIvC (ORCPT ); Wed, 21 Jul 2021 04:51:02 -0400 Received: from dggeme766-chm.china.huawei.com (unknown [172.30.72.54]) by szxga02-in.huawei.com (SkyGuard) with ESMTP id 4GV9G01tmTz7xbg; Wed, 21 Jul 2021 17:27:04 +0800 (CST) Received: from dggemi761-chm.china.huawei.com (10.1.198.147) by dggeme766-chm.china.huawei.com (10.3.19.112) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.2176.2; Wed, 21 Jul 2021 17:30:43 +0800 Received: from dggemi761-chm.china.huawei.com ([10.9.49.202]) by dggemi761-chm.china.huawei.com ([10.9.49.202]) with mapi id 15.01.2176.012; Wed, 21 Jul 2021 17:30:43 +0800 From: "Song Bao Hua (Barry Song)" To: Yury Norov CC: "andriy.shevchenko@linux.intel.com" , "gregkh@linuxfoundation.org" , "akpm@linux-foundation.org" , "linux-kernel@vger.kernel.org" , "dave.hansen@intel.com" , "linux@rasmusvillemoes.dk" , "rafael@kernel.org" , "rdunlap@infradead.org" , "agordeev@linux.ibm.com" , "sbrivio@redhat.com" , "jianpeng.ma@intel.com" , "valentin.schneider@arm.com" , "peterz@infradead.org" , "bristot@redhat.com" , "guodong.xu@linaro.org" , tangchengchang , "Zengtao (B)" , yangyicong , "tim.c.chen@linux.intel.com" , Linuxarm , "tiantao (H)" Subject: RE: [PATCH v7 2/4] topology: use bin_attribute to break the size limitation of cpumap ABI Thread-Topic: [PATCH v7 2/4] topology: use bin_attribute to break the size limitation of cpumap ABI Thread-Index: AQHXeXDlNwZNI9Wk4UqsPQdyS/XZkqtFQm+QgABABACAAMKqIP//k3qAgAOpXQCAAKbSAP//4B8AgAMmn3A= Date: Wed, 21 Jul 2021 09:30:43 +0000 Message-ID: <617707849f504158b1db320439b44247@hisilicon.com> References: <20210715115856.11304-1-song.bao.hua@hisilicon.com> <20210715115856.11304-3-song.bao.hua@hisilicon.com> <3d83c6b11dae4a83add9d8dcc04bbd80@hisilicon.com> <4ab537937f344893bf5bdcb13e46ce04@hisilicon.com> In-Reply-To: Accept-Language: en-GB, en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.126.202.118] Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8BIT MIME-Version: 1.0 X-CFilter-Loop: Reflected Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > -----Original Message----- > From: Yury Norov [mailto:yury.norov@gmail.com] > Sent: Tuesday, July 20, 2021 5:10 AM > To: Song Bao Hua (Barry Song) > Cc: andriy.shevchenko@linux.intel.com; gregkh@linuxfoundation.org; > akpm@linux-foundation.org; linux-kernel@vger.kernel.org; > dave.hansen@intel.com; linux@rasmusvillemoes.dk; rafael@kernel.org; > rdunlap@infradead.org; agordeev@linux.ibm.com; sbrivio@redhat.com; > jianpeng.ma@intel.com; valentin.schneider@arm.com; peterz@infradead.org; > bristot@redhat.com; guodong.xu@linaro.org; tangchengchang > ; Zengtao (B) ; > yangyicong ; tim.c.chen@linux.intel.com; Linuxarm > ; tiantao (H) > Subject: Re: [PATCH v7 2/4] topology: use bin_attribute to break the size > limitation of cpumap ABI > > On Mon, Jul 19, 2021 at 11:10:45AM +0000, Song Bao Hua (Barry Song) wrote: > > > > > > > -----Original Message----- > > > From: andriy.shevchenko@linux.intel.com > > > [mailto:andriy.shevchenko@linux.intel.com] > > > Sent: Monday, July 19, 2021 9:07 PM > > > To: Yury Norov > > > Cc: Song Bao Hua (Barry Song) ; > > > gregkh@linuxfoundation.org; akpm@linux-foundation.org; > > > linux-kernel@vger.kernel.org; dave.hansen@intel.com; > > > linux@rasmusvillemoes.dk; rafael@kernel.org; rdunlap@infradead.org; > > > agordeev@linux.ibm.com; sbrivio@redhat.com; jianpeng.ma@intel.com; > > > valentin.schneider@arm.com; peterz@infradead.org; bristot@redhat.com; > > > guodong.xu@linaro.org; tangchengchang ; > Zengtao (B) > > > ; yangyicong ; > > > tim.c.chen@linux.intel.com; Linuxarm ; tiantao (H) > > > > > > Subject: Re: [PATCH v7 2/4] topology: use bin_attribute to break the size > > > limitation of cpumap ABI > > > > > > On Fri, Jul 16, 2021 at 06:12:21PM -0700, Yury Norov wrote: > > > > On Sat, Jul 17, 2021 at 12:16:48AM +0000, Song Bao Hua (Barry Song) wrote: > > > > > > From: Yury Norov [mailto:yury.norov@gmail.com] > > > > > > Sent: Saturday, July 17, 2021 8:04 AM > > > > > > On Fri, Jul 16, 2021 at 08:49:58AM +0000, Song Bao Hua (Barry Song) > wrote: > > > > > > ... > > > > > > > > Generally good idea. However, for sysfs ABI entries, it might not be > > > > > that true. > > > > > > > > > > A sysfs entry might never be read for its whole life. As I explained > > > > > before, a sysfs entry - especially for list, is randomly "cat" by users. > > > > > Many of them won't be read forever. And after they are read once, they > > > > > will probably never be read again. The operations to read ABI could > be > > > > > random and rare. Performance wouldn't be a concern. > > > > > > > > > > To avoid holding the memory which might never be used, it is better > to > > > > > allocate and free the memory during runtime. I mean to allocate in show() > > > > > and free in show(), aka, to do it on demand. > > > > > > > > > > For example, for a server with 256CPU and each cpu has dozens of sysfs > ABI > > > > > entries, only a few of sysfs list entries might be randomly "cat" by > users. > > > > > Holding 256*entries memory doesn't look good. > > > > > > > > Ok, makes sense. > > > > > > > > > > This would require to add bitmap_max_string_size(list, bitmap, nbits), > > > > > > but it's O(1), and I think, others will find it helpful. > > > > > > > > > > What about getting size and memory at the same time? > > > > > > > > 1. We already have kasprintf() > > > > 2. It breaks coding style. > > > > > > > > Documentation/process/coding-style.rst: > > > > Functions should be short and sweet, and do just one thing. > > > > > > > > From practical point of view, there should be some balance between > > > > granularity and ease-of-use. But in this case, bitmap_list cries for > > > > a function that will help to estimate size of output buffer. > > > > > > According to the vsnprintf() logic the estimated size is what it returns. > If > > > user supplies too few bytes available, the comparison with the returned > value > > > can tell caller that space wasn't big enough. > > snprintf(NULL, 0, "pbl", ...) also works, but it's O(nbits), and user is not > guaranteed that allocated memory would be always sufficient. I mean max possible > length for given nbits, not a length of a specific string. > > In case of lists, the length may grow. Consider: > 0-8 -> 0-3,5-8 -> 0,2,4,6,8 > > If we want to allocate a storage for strings that may change, it would be > helpful to allocate memory for the lengthiest string in advance. > > So, bitmap_max_string_len() may be a convenient O(1) alternative for > those who interested in printing the same bitmap in the same buffer. > > > As far as my understanding, for estimated size in bitmap_max_string_size() > > Yury might mean something as below? > > > > * For bitmask: > > Each 32bit needs 9 bytes "11111111,", so the max size of mask would be: > > 9*nr_cpus / 32 ? > > 11111 -> "f1", but your formula gives 1. > I think it should be like this (not tested): > DIV_ROUND_UP(nbits, 4) + nbits < 32 ? 0 : nbits / 32 - 1 I am not quite sure this is correct, in case nbits=64, we will need: ffffffff,ffffffff 9+8=17 your formula is ignoring the "," for each 32bits? > > > * For list: > > Maximally cpu0-9 need 2bytes, like "1," > > Maximally cpu10-99 need 3bytes, like "50," > > Maximally cpu100-999 need 4bytes, like "101," > > Maximally cpu1000-9999 need 5 bytes.. > > > > So once we know the size of the bitmap, we can figure out the maximum > > size of its string for mask and list? > > > > Pls correct me if you don't mean this, yury. > > Assuming that longest possible strings are of the form 0,2,4,6,... I > think it's correct except for the last comma, so substract 1. I don't think 0,2,4,6,8 takes maximum length, 0-1,3-4,6-7 are longer. It seems maximum bitmap pattern is(binary): 110110110110... In this case, each 3bits takes 4 bytes. For cpu 10-99, it would be: 10-11,13-14,16-17,19-20, Each 3bits takes "6 bytes". For cpu100-999, it would be: 100-101, 103-104, 106-107,.... Each 3bits takes "8 bytes"? Anyway, It seems be quite tricky :-) > > If we decide to go on with this bitmap_max_strlen(), the list part > should be tested extensively. > Btw, sysfs core code needs changes to support pre-allocated memory in customized size and seq read on it. This needs a lot of efforts I am looking at. > > > > And it's > > > > easy to imagine a case where the estimated length of bitmap is needed > > > > explicitly: > > > > > > > > size_t max_size = bitmap_max_string_size(nbits); > > > > char *buf = kmalloc(PAGE_ALIGN(max_size) * nr_cpus); > > > > > > > > Thought, I don't insist. In your driver you can do: > > > > > > > > size_t size = snprintf(NULL, 0, ...); > > > > void *buf = kmalloc(size); > > > > > > > > It will be fully correct, and you already have everything you need. > > > > > > > > > ssize_t bitmap_get_print_buf(bool list, char **buf, const unsigned long > > > > > *maskp, int nmaskbits) > > > > > > > > > > ssize_t cpumap_get_print_buf(bool list, char **buf, const struct cpumask > > > *mask); > > > > > > > > > > This API returns the size of printed buffer, and it also gets the > > > > > printed result saved in *buf. Then drivers don't need to do three > > > > > steps: > > > > > > > > > > 1. get cpumap buffer size which is your cpumap_max_string_size() > > > > > 2. allocate memory for buffer according to size got in step 1 > > > > > 3. print bitmap(cpumap) to buffer by "pbl" > > > > > > > > > > It will only need to call bitmap_get_print_buf() and all three > > > > > things are done inside bitmap_get_print_buf(). > > > > > > > > > > How to use the size and memory allocated in cpumap_get_print_buf > > > > > will be totally up to users. > > > > > > > > > > The other benefit for this is that if we get string size during > initialization, > > > > > and then we print in show() entries, the size got at the beginning might > > > be not > > > > > enough as system topology might have changed. Sysfs ABI reflects the > status > > > of > > > > > system at this moment. > > > > > > -- > > > With Best Regards, > > > Andy Shevchenko > > > > > Thanks Barry