> Il giorno 19 apr 2017, alle ore 07:01, Bart Van Assche > <bart.vanass...@sandisk.com> ha scritto: > > On 04/11/17 00:29, Paolo Valente wrote: >> >>> Il giorno 10 apr 2017, alle ore 17:15, Bart Van Assche >>> <bart.vanass...@sandisk.com> ha scritto: >>> >>> On Mon, 2017-04-10 at 11:55 +0200, Paolo Valente wrote: >>>> That said, if you do always want maximum throughput, even at the >>>> expense of latency, then just switch off low-latency heuristics, i.e., >>>> set low_latency to 0. Depending on the device, setting slice_ilde to >>>> 0 may help a lot too (as well as with CFQ). If the throughput is >>>> still low also after forcing BFQ to an only-throughput mode, then you >>>> hit some bug, and I'll have a little more work to do ... >>> >>> Has it been considered to make applications tell the I/O scheduler >>> whether to optimize for latency or for throughput? It shouldn't be that >>> hard for window managers and shells to figure out whether or not a new >>> application that is being started is interactive or not. This would >>> require a mechanism that allows applications to provide such information >>> to the I/O scheduler. Wouldn't that be a better approach than the I/O >>> scheduler trying to guess whether or not an application is an interactive >>> application? >> >> IMO that would be an (or maybe the) optimal solution, in terms of both >> throughput and latency. We have even developed a prototype doing what >> you propose, for Android. Unfortunately, I have not yet succeeded in >> getting support, to turn it into candidate production code, or to make >> a similar solution for lsb-compliant systems. > > Hello Paolo, > > What API was used by the Android application to tell the I/O scheduler > to optimize for latency? Do you think that it would be sufficient if the > application uses the ioprio_set() system call to set the I/O priority to > IOPRIO_CLASS_RT? >
That's exactly the hack we are using in our prototype. However, it can only be a temporary hack, because it mixes two slightly different concepts: 1) the activation of weight raising and other mechanisms for reducing latency for the target app, 2) the assignment of a different priority class, which (cleanly) means just that processes in a lower priority class will be served only when the processes of the target app have no pending I/O request. Finding a clean boosting API would be one of the main steps to turn our prototype into a usable solution. Thanks, Paolo > Thanks, > > Bart.
