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Date: Fri, 08 Jun 2007 06:54:30 +0200 From: Eric Dumazet <dada1@...mosbay.com> To: Davide Libenzi <davidel@...ilserver.org> CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Andrew Morton <akpm@...ux-foundation.org>, Ulrich Drepper <drepper@...hat.com>, Ingo Molnar <mingo@...e.hu> Subject: Re: [patch 1/8] fdmap v2 - fdmap core Davide Libenzi a écrit : > +struct fd_map { > + struct fd_map *next; > + struct rcu_head rcu; > + unsigned int base; > + unsigned int size; > + struct list_head slist; > + struct list_head *slots; > + unsigned int fdnext; > + unsigned long *map; > + void (*freecb)(void *, struct fd_map *); > + void *freecb_priv; > +}; On x86_64 that would mean folowing offsets struct fd_map { struct fd_map *next; /* 0 */ struct rcu_head rcu; /* 8 */ unsigned int base; /* 0x18 */ unsigned int size; /* 0x1c */ struct list_head slist; /* 0x20 */ struct list_head *slots; /* 0x30 */ unsigned int fdnext; /* 0x38 */ unsigned long *map; /* 0x40 */ void (*freecb)(void *, struct fd_map *); /* 0x48 */ void *freecb_priv; /* 0x50 */ }; /* size 0x58 */ As L1_CACHE_BYTES is 64, two cache lines are necessary to get base,size,map And a change of fdnext dirties one cache line that should be kept read only to avoid false sharing. I suggest to reorder to move rcu and next at the end (since they are seldom used). Also move fdnext on a separate cache line on SMP struct fd_map { /* * read mostly part */ unsigned int base; /* 0x00 */ unsigned int size; /* 0x04 */ struct list_head slist; /* 0x08 */ struct list_head *slots; /* 0x18 */ unsigned long *map; /* 0x28 */ void (*freecb)(void *, struct fd_map *); /* 0x30 */ void *freecb_priv; /* 0x38 */ /* * written part on a separate cache line in SMP */ unsigned int fdnext ____cacheline_aligned_in_smp; /* 0x40 */ struct fd_map *next; /* 0x48 */ struct rcu_head rcu; /* 0x50 */ }; Thank you - 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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