Messages in this thread Patch in this message | | | Date | Thu, 7 Mar 2013 10:32:40 +0000 | From | Eric Wong <> | Subject | Re: [PATCH] epoll: trim epitem by one cache line on x86_64 |
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Andrew Morton <akpm@linux-foundation.org> wrote: > It's going to be hard to maintain this - someone will change something > sometime and break it. I suppose we could add a runtime check if we > cared enough. Adding a big fat comment to struct epitem might help.
Thanks for looking at this patch. I'll send a patch with a comment about keeping epitem size in check. Also, would adding (with comments):
BUILD_BUG_ON(sizeof(struct epitem) > 128);
...be too heavy-handed? I used that in my testing. I'll check for: sizeof(void *) <= 8 too; in case 128-bit machines appear...
> I don't see much additional room to be saved. We could probably remove > epitem.nwait, but that wouldn't actually save anything because nwait > nestles with ffd.fd.
If we remove nwait, we can move epoll_event up and have event.events tucked in there. I have more and more depending on epoll, so I'll be around to comment on future epoll changes as they come up.
> I tested your patch on powerpc and it reduced sizeof(epitem) from 136 > to 128 for that arch as well, so I suggest we run with > > --- a/fs/eventpoll.c~epoll-trim-epitem-by-one-cache-line-on-x86_64-fix > +++ a/fs/eventpoll.c > @@ -105,7 +105,7 @@ > struct epoll_filefd { > struct file *file; > int fd; > -} EPOLL_PACKED; > +} __packed;
Thanks for testing on ppc. Looks good to me. For what it's worth: Acked-by: Eric Wong <normalperson@yhbt.net>
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