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Date: Fri, 12 Dec 2008 08:07:23 +0100 From: Eric Dumazet <dada1@...mosbay.com> To: Nick Piggin <npiggin@...e.de> CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linux Memory Management List <linux-mm@...ck.org> Subject: Re: [rfc][patch] SLQB slab allocator Nick Piggin a écrit : > On Fri, Dec 12, 2008 at 06:38:26AM +0100, Eric Dumazet wrote: >> Nick Piggin a écrit : >>> I'm going to continue working on this as I get time, and I plan to soon ask >>> to have it merged. It would be great if people could comment or test it. >>> >> It seems really good, but will need some hours to review :) >> >> Minor nit : You spelled Qeued instead of Queued in init/Kconfig >> >> +config SLQB >> + bool "SLQB (Qeued allocator)" > > OK, thanks. > > >> One of the problem I see with SLAB & SLUB is the irq masking stuff. >> Some (many ???) kmem_cache are only used in process context, I see no point of >> disabling irqs for them. > > That's a very good point actually, and something I want to look at... > > I'm thinking it will make most sense to provide a > kmem_cache_alloc/free_irqsafe for callers who either don't do any > interrupt context allocations, or already have irqs off (another > slab flag will just add another branch in the fastpaths). > > And then also a kmalloc/kfree_irqsoff for code which already has > irqs off. > > That's something which benefit all slab allocators roughly equally, > so at the moment I'm concentrating on the core code. But it's a very > good idea. > > >> I tested your patch on my 8 ways HP BL460c G1, on top >> on my last patch serie. (linux-2.6, not net-next-2.6) >> >> # time ./socketallocbench >> >> real 0m1.300s >> user 0m0.078s >> sys 0m1.207s >> # time ./socketallocbench -n 8 >> >> real 0m1.686s >> user 0m0.614s >> sys 0m12.737s >> >> So no bad effect (same than SLUB). > > Cool, thanks. > > >> For the record, SLAB is really really bad for this workload >> >> PU: Core 2, speed 3000.1 MHz (estimated) >> Counted CPU_CLK_UNHALTED events (Clock cycles when not halted) with a unit mask of 0x00 (Unhalted core cycles) count 100 >> 000 >> samples cum. samples % cum. % symbol name >> 136537 136537 10.8300 10.8300 kmem_cache_alloc >> 129380 265917 10.2623 21.0924 tcp_close >> 79696 345613 6.3214 27.4138 tcp_v4_init_sock >> 73873 419486 5.8596 33.2733 tcp_v4_destroy_sock >> 63436 482922 5.0317 38.3050 sysenter_past_esp >> 62140 545062 4.9289 43.2339 inet_csk_destroy_sock >> 56565 601627 4.4867 47.7206 kmem_cache_free >> 40430 642057 3.2069 50.9275 __percpu_counter_add >> 35742 677799 2.8350 53.7626 init_timer >> 35611 713410 2.8246 56.5872 copy_from_user >> 21616 735026 1.7146 58.3018 d_alloc >> 20821 755847 1.6515 59.9533 alloc_inode >> 19645 775492 1.5582 61.5115 alloc_fd >> 18935 794427 1.5019 63.0134 __fput >> 18922 813349 1.5009 64.5143 inet_create >> 18919 832268 1.5006 66.0149 sys_close >> 16074 848342 1.2750 67.2899 release_sock >> 15337 863679 1.2165 68.5064 lock_sock_nested >> 15172 878851 1.2034 69.7099 sock_init_data >> 14196 893047 1.1260 70.8359 fd_install >> 13677 906724 1.0849 71.9207 drop_file_write_access >> 13195 919919 1.0466 72.9673 dput >> 12768 932687 1.0127 73.9801 inotify_d_instantiate >> 11404 944091 0.9046 74.8846 init_waitqueue_head >> 11228 955319 0.8906 75.7752 sysenter_do_call >> 11213 966532 0.8894 76.6647 local_bh_enable_ip >> 10948 977480 0.8684 77.5330 __sock_create >> 10912 988392 0.8655 78.3986 local_bh_enable >> 10665 999057 0.8459 79.2445 __new_inode >> 10579 1009636 0.8391 80.0836 inet_release >> 9665 1019301 0.7666 80.8503 iput_single >> 9545 1028846 0.7571 81.6074 fput >> 7950 1036796 0.6306 82.2379 sock_release >> 7236 1044032 0.5740 82.8119 local_bh_disable >> >> >> We can see most of the time is taken by the memset() to clear object, >> then irq masking stuff... > > Yep, it's difficult to make the local alloc/free fastpath much more > optimal as-is. > > Is SLAB still bad at the test with the slab-rcu patch in place? > SLAB has a pretty optimal fastpath as well, although if its queues > start overflowing, it can run into contention quite easily. Yes, I forgot I applied Christoph patch (SLAB_DESTROY_BY_RCU for struct file) in the meantime, silly me, this was with the v2 of my serie, with only 5 patches. With SLAB, results are quite good ! # time ./socketallocbench real 0m1.201s user 0m0.071s sys 0m1.122s # time ./socketallocbench -n8 real 0m1.616s user 0m0.578s sys 0m12.220s > >> c0281e10 <kmem_cache_alloc>: /* kmem_cache_alloc total: 140659 10.8277 */ > > I guess you're compiling with -Os? I find gcc can pack the fastpath > much better with -O2, and actually decrease the effective icache > footprint size even if the total text size increases... No, I dont use -Os, unless something got wrong # CONFIG_CC_OPTIMIZE_FOR_SIZE is not set # CONFIG_OPTIMIZE_INLINING is not set -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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