8b09116a5a
possible future I-cache coherency operation can succeed. On ARM for example the L1 cache can be (is) virtually mapped, which means that any I/O that uses temporary mappings will not see the I-cache made coherent. On ia64 a similar behaviour has been observed. By flushing the D-cache, execution of binaries backed by md(4) and/or NFS work reliably. For Book-E (powerpc), execution over NFS exhibits SIGILL once in a while as well, though cpu_flush_dcache() hasn't been implemented yet. Doing an explicit D-cache flush as part of the non-DMA based I/O read operation eliminates the need to do it as part of the I-cache coherency operation itself and as such avoids pessimizing the DMA-based I/O read operations for which D-cache are already flushed/invalidated. It also allows future optimizations whereby the bcopy() followed by the D-cache flush can be integrated in a single operation, which could be implemented using on-chips DMA engines, by-passing the D-cache altogether. |
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