From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <47EA7958.6050202@sgi.com> Date: Wed, 26 Mar 2008 09:27:04 -0700 From: Mike Travis MIME-Version: 1.0 Subject: Re: [PATCH 06/10] x86: reduce memory and stack usage in intel_cacheinfo References: <20080325220650.835342000@polaris-admin.engr.sgi.com> <20080325220651.683748000@polaris-admin.engr.sgi.com> <20080326065023.GG18301@elte.hu> <47EA6EA3.1070609@sgi.com> <47EA7633.1080909@goop.org> In-Reply-To: <47EA7633.1080909@goop.org> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Jeremy Fitzhardinge Cc: Ingo Molnar , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" List-ID: Jeremy Fitzhardinge wrote: > Mike Travis wrote: >> Ingo Molnar wrote: >> >>> * Mike Travis wrote: >>> >>> >>>> * Change the following static arrays sized by NR_CPUS to >>>> per_cpu data variables: >>>> >>>> _cpuid4_info *cpuid4_info[NR_CPUS]; >>>> _index_kobject *index_kobject[NR_CPUS]; >>>> kobject * cache_kobject[NR_CPUS]; >>>> >>>> * Remove the local NR_CPUS array with a kmalloc'd region in >>>> show_shared_cpu_map(). >>>> >>> thanks Travis, i've applied this to x86.git. >>> >>> one observation: >>> >>> >>>> static ssize_t show_shared_cpu_map(struct _cpuid4_info *this_leaf, >>>> char *buf) >>>> { >>>> - char mask_str[NR_CPUS]; >>>> - cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map); >>>> - return sprintf(buf, "%s\n", mask_str); >>>> + int n = 0; >>>> + int len = cpumask_scnprintf_len(nr_cpu_ids); >>>> + char *mask_str = kmalloc(len, GFP_KERNEL); >>>> + >>>> + if (mask_str) { >>>> + cpumask_scnprintf(mask_str, len, this_leaf->shared_cpu_map); >>>> + n = sprintf(buf, "%s\n", mask_str); >>>> + kfree(mask_str); >>>> + } >>>> + return n; >>>> >>> the other changes look good, but this one looks a bit ugly and >>> complex. We basically want to sprintf shared_cpu_map into 'buf', but >>> we do that by first allocating a temporary buffer, print a string >>> into it, then print that string into another buffer ... >>> >>> this very much smells like an API bug in cpumask_scnprintf() - why >>> dont you create a cpumask_scnprintf_ptr() API that takes a pointer to >>> a cpumask? Then this change would become a trivial and much more >>> readable: >>> >>> - char mask_str[NR_CPUS]; >>> - cpumask_scnprintf(mask_str, NR_CPUS, this_leaf->shared_cpu_map); >>> - return sprintf(buf, "%s\n", mask_str); >>> + return cpumask_scnprintf_ptr(buf, NR_CPUS, >>> &this_leaf->shared_cpu_map); >>> >>> Ingo >>> >> >> The main goal was to avoid allocating 4096 bytes when only 32 would do >> (characters needed to represent nr_cpu_ids cpus instead of NR_CPUS cpus.) >> But I'll look at cleaning it up a bit more. It wouldn't have to be >> a function if CHUNKSZ in cpumask_scnprintf() were visible (or a >> non-changeable >> constant.) >> > > It's a pity you can't take advantage of kasprintf to handle all this. > > Hm, I would say that bitmap_scnprintf is a candidate for implementation > as a printk format specifier so you could get away from needing a > special function to print bitmaps... Hmm, I hadn't thought of that. There is commonly a format spec called %b for diags, etc. to print bit strings. Maybe something like: "... %*b ...", nr_cpu_ids, ptr_to_bitmap where the length arg is rounded up to 32 or 64 bits...? > > Eh? What's the difference between snprintf and scnprintf? Good question... I'll have to ask the cpumask person. ;-) > > J Thanks! Mike -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org