On Wed, Sep 30, 2015 at 03:39:52PM +1000, Neil Brown wrote: > Christoph Hellwig <hch@xxxxxx> writes: > > > So the summary is that for now you want me to resend with a patch > > to opt into using FUA? > > I'd like to avoid "opt in" if at all possible. > Shoahua measured that using "FUA" for all writes to the journal > hurt performance on at least one device. Do you have a different device > where it demonstrably helps? > If there any chance of automatically detecting which is which? I have a high end SAS SSD where it helps, but the real use case where it makes a major difference are battery backed dimms (NV-DIMMS) or other devices where we don't even need the FUA bit as they don't have a cache at all. The important part is to avoid the batching up for the non-existant flush in that case. So I could defintively default the code to on only for those, but not even allowing a tunable for devices that have the FUA bit seems like an odd restriction. -- To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
