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Date: Tue, 03 Apr 2007 07:11:28 +0000 From: "Paa Paa" <paapaa125@...mail.com> To: linux-kernel@...r.kernel.org Subject: Lower HD transfer rate with NCQ enabled? I'm using Linux 2.6.20.4. I noticed that I get lower SATA hard drive throughput with 2.6.20.4 than with 2.6.19. The reason was that 2.6.20 enables NCQ by defauly (queue_depth = 31/32 instead of 0/32). Transfer rate was measured using "hdparm -t": With NCQ (queue_depth == 31): 50MB/s. Without NCQ (queue_depth == 0): 60MB/s. 20% difference is quite a lot. This is with Intel ICH8R controller and Western Digital WD1600YS hard disk in AHCI mode. I also used the next command to cat-copy a biggish (540MB) file and time it: rm temp && sync && time sh -c 'cat quite_big_file > temp && sync' Here I noticed no differences at all with and without NCQ. The times (real time) were basically the same in many successive runs. Around 19s. Q: What conclusion can I make on "hdparm -t" results or can I make any conclusions? Do I really have lower performance with NCQ or not? If I do, is this because of my HD or because of kernel? Best regards, Paapaa _________________________________________________________________ Express yourself instantly with MSN Messenger! Download today it's FREE! http://messenger.msn.click-url.com/go/onm00200471ave/direct/01/ - 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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