On Tue, 26 May 2015 16:34:14 +0100 Alasdair G Kergon <agk@xxxxxxxxxx> wrote: > On Tue, May 26, 2015 at 08:02:08AM -0700, Ming Lin wrote: > > Now bio_add_page() can build lager bios. > > And blk_queue_split() can split the bios in ->make_request() if needed. > > But why not try to make the bio the right size in the first place so you > don't have to incur the performance impact of splitting? Because we don't know what the "right" size is. And the "right" size can change when array reconfiguration happens. Splitting has to happen somewhere, if only in bio_addpage where it decides to create a new bio rather than add another page to the current one. So moving the split to a different level of the stack shouldn't necessarily change the performance profile. Obviously testing is important to confirm that. NeilBrown > > What performance testing have you yet done to demonstrate the *actual* impact > of this patchset in situations where merge_bvec_fn is currently a net benefit? > > Alasdair > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > 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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