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On Tue, Oct 17, 2006 at 03:23:13PM +0200, Jens Axboe wrote: > On Tue, Oct 17 2006, Arjan van de Ven wrote: ... > > Hi, > > > > it's a nice idea in theory. However... since IO bandwidth for seeks is > > about 1% to 3% of that of sequential IO (on disks at least), which > > bandwidth do you want to allocate? "worst case" you need to use the > > all-seeks bandwidth, but that's so far away from "best case" that it may > > well not be relevant in practice. Yet there are real world cases where > > for a period of time you approach worst case behavior ;( > > Bandwidth reservation would have to be confined to special cases, you > obviously cannot do it "in general" for the reasons Arjan lists above. How about allocating I/O operations instead of bandwidth ? So, any read is really a seek+read, and we count that as one I/O operation. Same for writes. Since the total "capacity" of the system is typically (in real-world scenarios) the number of operations (seek+X) rather than the raw sequential bandwidth anyway, I suppose that I/O operations would be what you wanted to allocate anyway. Anyway, just a thought... (And if you're thinking one sequential reader/writer could then starve the system; well, count every 256KiB of data to read/write as a seperate I/O operation even though no seek is needed. That would very roughly match the raw read/write performance with the seek performance) -- / jakob - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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