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For better explanation, I break down the page fault handling into steps: 1) There is a page fault caused by DMA operation initiated by SPU and DMA is suspended. 2) The interrupt handler 'spu_irq_class_1()/__spu_trap_data_map()' is called and it just wakes up the sleeping spe-manager thread. 3) by PPE scheduler, the corresponding bottom half, spu_irq_class_1_bottom() is called in process context and DMA is restarted. There can be a quite large time gap between 2) and 3) and I found the following problem: Between 2) and 3) If the context becomes unbound, 3) is not executed because when the spe-manager thread is awaken, the context is already saved. (This situation can happen, for example, when a high priority spe thread newly started in that time gap) But the actual problem is that the corresponding SPU context does not work even if it is bound again to a SPU. Besides I can see the following warning in mambo simulator when the context becomes unbound(in save_mfc_cmd()), i.e. when unbind() is called for the context after step 2) before 3) : 'WARNING: 61392752237: SPE2: MFC_CMD_QUEUE channel count of 15 is inconsistent with number of available DMA queue entries of 16' After I go through available documents, I found that the problem is because the suspended DMA is not restarted when it is bound again. Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com> Signed-off-by: Paul Mackerras <paulus@samba.org> |
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