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 Received: from mails.dpdk.org (mails.dpdk.org [217.70.189.124]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F3BAC4332F for ; Mon, 12 Dec 2022 12:03:55 +0000 (UTC) Received: from mails.dpdk.org (localhost [127.0.0.1]) by mails.dpdk.org (Postfix) with ESMTP id 2340F4021D; Mon, 12 Dec 2022 13:03:54 +0100 (CET) Received: from smartserver.smartsharesystems.com (smartserver.smartsharesystems.com [77.243.40.215]) by mails.dpdk.org (Postfix) with ESMTP id 9D54E40151 for ; Mon, 12 Dec 2022 13:03:53 +0100 (CET) Content-class: urn:content-classes:message Subject: RE: [PATCH V3 00/11] telemetry: add u32 value type and hex integer string API MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Date: Mon, 12 Dec 2022 13:03:52 +0100 X-MimeOLE: Produced By Microsoft Exchange V6.5 Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D87586@smartserver.smartshare.dk> In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [PATCH V3 00/11] telemetry: add u32 value type and hex integer string API Thread-Index: AdkOG9kOneUNivazTdem/l4hI/YzDgAAnHxw References: <20221208080540.62913-1-lihuisong@huawei.com> <20221212064306.39232-1-lihuisong@huawei.com> <98CBD80474FA8B44BF855DF32C47DC35D87585@smartserver.smartshare.dk> From: =?iso-8859-1?Q?Morten_Br=F8rup?= To: "Bruce Richardson" , "Huisong Li" Cc: , , , , X-BeenThere: dev@dpdk.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: DPDK patches and discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dev-bounces@dpdk.org > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > Sent: Monday, 12 December 2022 12.21 >=20 > On Mon, Dec 12, 2022 at 12:02:32PM +0100, Morten Br=F8rup wrote: > > > From: Bruce Richardson [mailto:bruce.richardson@intel.com] > > > Sent: Monday, 12 December 2022 11.32 > > > > > > On Mon, Dec 12, 2022 at 02:42:55PM +0800, Huisong Li wrote: > > > > Some lib telemetry interfaces add the 'u32' and 'u64' data by = the > > > > rte_tel_data_add_dict/array_int API. This may cause data > conversion > > > error > > > > or data truncation. > > > > > > > > The 'u32' data can not be assigned to signed 32-bit integer. > However, > > > > assigning to u64 is very wasteful, after all, the buffer = capacity > of > > > each > > > > transfer is limited. So it is necessary for 'u32' data to add > usigned > > > > 32-bit integer type and a series of 'u32' operation APIs. > > > > > > > > This patchset uses the new 'u32' API to resolve the problem of > data > > > > conversion error, and use the 'u64' API to add 'u64' data. > > > > > > > > In addition, this patchset introduces two APIs to store u32 and > u64 > > > > values as hexadecimal encoded strings in telemetry library. > > > > > > > > --- -v3: fix a misspelling mistake in commit log. -v2: - fix = ABI > > > break > > > > warning. - introduce two APIs to store u32 and u64 values as > > > hexadecimal > > > > encoded strings. > > > > > > > I'm not convinced about adding the u32 value generically to the > > > telemetry > > > lib - except in the case of having explicit function calls for u32 > vs > > > u64 > > > hex strings. Having a u32 type doesn't gain us any space = internally > > > over a > > > u64 value, since all values are in a union type. Also, for output > as > > > json, > > > the numeric values are all output as decimal values, meaning that > the > > > value > > > 1 appears as the same size in the output string whether it is a = u32 > or > > > u64 > > > type. Now, it may save space in a future binary output format, but > even > > > then it still may not do so. > > > > I agree that a u32 doesn't gain any space internally. > > > > However, many SNMP counters are unsigned 32 bit, and expected to = wrap > around as such. > > > > So I suppose the u32 type might be useful for SNMP, if obtained > through the telemetry library. > > > > Alternatively, we could somehow reuse the u64 type and require the > application to pass (value & UINT32_MAX) to the u64 functions. To make > this easy to use, we should add some wrappers to do it for the > application. And eventually we would probably end up with something > very similar to this patch. > > >=20 > I think just using the u64 functions is probably simplest and best > right > now. If we add support for something like snmp then yes, it would make > sense to explicitly add it, but it seems like a lot of extra code for > little or no benefit until we support something like that. If we wanted to fix this generally, we should rely on type promotion, so = the existing _int function should be updated to take an int64_t value, = and the _u64 function should be renamed to _uint (and still take an = uint64_t value). However, that would break the ABI, and would need to go = through some process for that. So let's not change this now. I tend to agree with Bruce on this: Let's get rid of the new u32 = functions, and rely on the u64 functions for that instead. >=20 > > > > > > Therefore, I'd tend to keep the existing u64 type as-is, and > instead > > > only > > > add the functions for outputting hex values. Those hex output > functions > > > could take an additional parameter indicating the desired hex > output > > > length, as there could well be cases where we want just 16-bit hex > > > value > > > too. > > > > The way I read the patch series, the hex output length is not fixed, > but an u64 value of 5 will be output as 0x5, not 0x0000000000000005. > > > > So the only benefit of having both u32_hex and u64_hex functions is > to avoid type promotion from uint32_t to uint64_t on input for 32 bit > values. > > > > Instead of passing a 3rd parameter or adding u16_hex functions, we > could consider just having one set of hex functions using uint64_t for > the value, and rely on type promotion for 32 and 16 bit values. > > >=20 > +1 to having only a single hex function, and I think type promotion > should > work fine. >=20 > However, I still think it might be worthwhile allowing the user to = pass > in > a min output length parameter too. I find for many hex strings having > the > leading zeros to explicitly show the length can be useful. The value > "0" > could cover the current behaviour of no-padding, otherwise the > parameter > should indicate the number of bits to be displayed. (If we want to = lock > it > down we can use an enum parameter rather than int to limit it to 0, 8, > 16, > 32 or 64 bit displayed values). An extra parameter for minimum output length (in number of input bits) = would be very nice, and makes avoids a set of functions for each bit = width. (I don't think it should be lock it down to some special bit lengths; = there is no need to prevent 24 bit or other exotic bit widths.) Something like this: char str[64]; // Big enough length. if (bits !=3D 0) { char format[16]; // Big enough length. sprintf(format, "0x0%u%" PRIx64, (bits + 3) / 4); sprintf(str, format, value); } else { sprintf(str, "0x%" PRIx64, value); } >=20 > All that said, I'm not massively concerned if we want to just keep the > current approach of always just printing without any leading zeros. > It's a > nice-to-have only for me. >=20 > /Bruce