Messages in this thread | | | Date | Wed, 7 Sep 2011 14:27:49 -0400 | From | Konrad Rzeszutek Wilk <> | Subject | Re: Help with implementing some form of barriers in 3.0 kernels. |
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On Wed, Sep 07, 2011 at 02:17:40PM -0400, Vivek Goyal wrote: > On Wed, Sep 07, 2011 at 01:48:32PM -0400, Konrad Rzeszutek Wilk wrote: > > Hey Christoph, > > > > I was wondering what you think is the proper way of implementing a > > backend to support the 'barrier' type requests? We have this issue were > > there are 2.6.36 type guests that still use barriers and we would like > > to support them properly. But in 3.0 there are no barriers - hence > > the question whether WRITE_fLUSH_FUA would be equal to WRITE_BARRIER? > > I think WRITE_FLUSH_FUA is not same as WRITE_BARRIER. Because it does > not ensure request ordering. A request rq2 which is issued after rq1 (with > WRITE_flush_FUA), can still finish before rq1. In the past WRITE_BARRIER > would not allow that. > > So AFAIK, WRITE_flush_fua is not WRITE_BARRIER.
Ok, any thoughts on how to emulate it then perhaps? Mark each request after rq1 with WRITE_FUA? .. But then how long should the _FUA bit be set - perhaps until the rq1 has completed?
> > Thanks > Vivek
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