Messages in this thread | | | Date | Tue, 13 Feb 2007 12:27:14 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCH 2.6.21 review I] [21/25] x86_64: a memcpy that tries to reduce cache pressure |
| |
Andi Kleen a écrit : > From: "Bryan O'Sullivan" <bos@pathscale.com> > > This copy routine is memcpy-compatible, but on some architectures will use > cache-bypassing loads to avoid bringing the source data into the cache. > > One case where this is useful is when a device issues a DMA to a memory > region, and the CPU must copy the DMAed data elsewhere before doing any work > with it. Since the source data is read-once, write-never from the CPU's > perspective, caching the data at those addresses can only evict potentially > useful data. > > We provide an x86_64 implementation that uses SSE non-temporal loads, and a > generic version that falls back to plain memcpy.
> + movq %r11, 56(%rdi) > + addq %rcx, %rdi > + cmpq %rdx, %rcx /* is rdx >= 64? */ > + jbe .L42 > + sfence > + orl %edx, %edx > + je .L33
I have three questions/remarks
1) Just curious why sfence is necessary here ?
2) Shouldnt we use this for large buffers, and restrict them to a size multiple of 64, to avoid all these conditional branches ?
3) Also, the first 128 bytes of the source buffer will be bring into cache.
- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |