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Message-ID: <a39687c7cc1c7137f0187aea4ee38676@assyoma.it> Date: Thu, 11 Sep 2014 16:32:00 +0200 From: Gionatan Danti <g.danti@...yoma.it> To: linux-kernel@...r.kernel.org Cc: g.danti@...yoma.it Subject: AHCI maximum transfer size Hi all, I searched the list and the internet for this question, but I did not find a definitive answer. I wonder what is the maximum AHCI transfer size for kernel 2.6.32.x Let me explain: using a command as "dd if=/dev/zero of=/dev/sda bs=2M" I can see, via iostat, that request-size is at 2M (as expected). However it seems to me that the effective transfer size is way lower: disabling writeback cache on the target disk, I see very low performance even for big-chunk transfers. Googling, I found this post on stackoverflow stating that maximum observerd AHCI transfer size (with a SATA protocol analyzer) is 128KB: http://stackoverflow.com/questions/24053662/how-to-enlarge-sata-transfer-size-in-linux-ahci-driver. The stackoverflow post seems to agree with this old LWN.net article: http://lwn.net/Articles/77981/ Anyone has any idea of how to find (and eventually change) the used AHCI transfer size without touching the code? NOTE: please CC me directly. Regards. -- Danti Gionatan Supporto Tecnico Assyoma S.r.l. - www.assyoma.it email: g.danti@...yoma.it - info@...yoma.it GPG public key ID: FF5F32A8 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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