On 10/17/2016 11:00 AM, SF Markus Elfring wrote: >>> Calling the function "seq_putc" will be more efficient than "seq_printf" >>> in this case because of the following reasons. >>> >>> 1. How does the distribution look like for supported processor architectures >>> where the data transfer for bytes (as a function call parameter) >>> is faster than for (string) pointers? >>> >> How would I know? > > How many processor architecture characteristics do you know already? > x86, s390x, ppc/ppc64. > * Is a string pointer often longer than a byte? > Always. (Which up to now I thought was basic programming knowledge...) > * I imagine that it can become also interesting to check byte level data access > under constraints of machine word sizes and alignment. > So, another test for you to do. > >> I would assume that _you_ did some measurements here; > > How much would you trust in any concrete numbers I could present > for this use case? > > Do you give more trust to a reference testing platform? > At the moment _any_ test would do. With every response from your side you just keep on asking further questions. But so far you haven't delivered any answers nor measurements. > >> I could easily claim that seq_printf() is more efficient than >> seq_putc(), and won't apply your patch. > > This is also possible in principle. > No, this is what's going to happen if you don't show any measurements. > >> So _you_ have to prove that your patch is more efficient. > > How many results would we like to clarify from various hardware > and software combinations? > See above. At the moment _any_ test result from your side would do. > >>> 2. Did anybody measure already how many the execution times can vary >>> for these functions? >>> >> Probably not. > > Thanks for this information. > > How important are the mentioned functions for you within the Linux > programming interface so far? > Not very. The interface is only used in a slow path, and the execution time doesn't affect I/O performance in any way. > >> Unless _you_ prove that _your_ patch is more efficient it won't get applied. > > Which data would you accept as a "prove" in this case? > Again: You want something from us. We don't have to prove anything, you need to convince us. And it is really hard to convince anyone by asking questions. > >>> Where do you get doubts about its efficiency for the data processing >>> of a single character? >>> >> Because it's being called at the end of a function calling seq_printf() already. > > Interesting view … > > >> So exchanging a single call is probably not helping anything, >> as the compiler will optimize it anyway. > > How common is the discussed software transformation between implementations > for optimising compilers? > > >> Case in point: with your patch the x86_64 compiler generates nearly >> identical code for driver/md/raid1.c, but with one instruction _more_ >> after your patch has been applied. > > Which software versions and command parameters did you try out > for this information (from an unspecified run time environment)? > > # gcc --version gcc (SUSE Linux) 4.8.5 Copyright (C) 2015 Free Software Foundation, Inc. This is free software; see the source for copying conditions. There is NO warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. git tree from git.kernel.org/mkp/u/4.10/scsi-queue _I_ did some measurements. I'm still waiting from results from your side. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
