On 2015/6/8 18:42, Vinod Koul wrote: > On Tue, Jun 02, 2015 at 02:37:31PM +0800, Jiang Liu wrote: >> Ccing Rafael, it's ACPI hotplug related. >> >> On 2015/6/2 14:36, Jiang Liu wrote: >>> The dmaengine core assumes that async DMA devices will only be removed >>> when they not used anymore, or it assumes dma_async_device_unregister() >>> will only be called by dma driver exit routines. But this assumption is >>> not true for the IOAT driver, which calls dma_async_device_unregister() >>> from ioat_remove(). So current IOAT driver doesn't support device >>> hot-removal because it may cause system crash to hot-remove an inuse >>> IOAT device. >>> >>> To support CPU socket hot-removal, all PCI devices, including IOAT >>> devices embedded in the socket, will be hot-removed. The idea solution >>> is to enhance the dmaengine core and IOAT driver to support hot-removal, >>> but that's too hard. >>> >>> This patch implements a hack to disable IOAT devices under hotplug-capable >>> CPU socket so it won't break socket hot-removal. >>> > So below looks okay though I wonder how hard would it be to fix hot unplug ? Hi Vinod, Thanks for review. About three years ago I worked out a patch set to enhance the dmaengine core and ioat device driver to support hot-removal. But it has been rejected due to concerns about performance penalty caused by usage tracking. To support hot-removal, we need to track dma channel usage and a way to reclaim dma channels when hot-removing. This may cause sensible performance penalty. Recently I have tried again but still haven't find a way to support hot-removal. So eventually I suggest to disable IOAT device on hot-plug capable systems. Thanks! Gerry -- To unsubscribe from this list: send the line "unsubscribe dmaengine" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
