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Date: Tue, 2 Dec 2008 17:25:04 -0500 (EST) From: Steven Rostedt <rostedt@...dmis.org> To: Andrew Morton <akpm@...ux-foundation.org> cc: linux-kernel@...r.kernel.org, mingo@...e.hu, fweisbec@...il.com, srostedt@...hat.com, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: [PATCH 3/5] ring-buffer: read page interface On Tue, 2 Dec 2008, Andrew Morton wrote: > On Tue, 02 Dec 2008 15:34:07 -0500 > Steven Rostedt <rostedt@...dmis.org> wrote: > > > From: Steven Rostedt <srostedt@...hat.com> > > > > Impact: new API to ring buffer > > > > This patch adds a new interface into the ring buffer that allows a > > page to be read from the ring buffer on a given CPU. For every page > > read, one must also be given to allow for a "swap" of the pages. > > > > rpage = ring_buffer_alloc_read_page(buffer); > > if (!rpage) > > goto err; > > ret = ring_buffer_read_page(buffer, &rpage, cpu, full); > > if (!ret) > > goto empty; > > process_page(rpage); > > ring_buffer_free_read_page(rpage); > > > > The caller of these functions must handle any waits that are > > needed to wait for new data. The ring_buffer_read_page will simply > > return 0 if there is no data, or if "full" is set and the writer > > is still on the current page. > > > > ... > > > > +static inline void * > > +__rb_data_page_index(struct buffer_data_page *page, unsigned index) > > +{ > > + return page->data + index; > > +} > > Many kernel developers will fall over stunned and confused when they > see a variable called `page' which does not have type `struct page *'. > This is a very strong kernel convention and this code tromps all over > it :( > > How's about renaming all of these everywhere to `bpage' or whatever? OK, I'll send a patch to Ingo to make this update. > > > > > ... > > > > + if (!local_read(&cpu_buffer->reader_page->page->commit)) > > > > Rusty (I think it was Rusty) has convincingly argued that local_t is > irredeemably busted. I forget the details? Really?? I've been using local for quite a bit. Using atomic seems overkill, since I only want to be able to protect against updates by interrupts. Perhaps what needs to be done is to fix local? -- Steve -- 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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