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[Erlug] Accesso dischi: 2.2.17 contro 2.4.9

To: erlug@xxxxxxxxxxxxxx
Subject: [Erlug] Accesso dischi: 2.2.17 contro 2.4.9
From: Davide Bolcioni <se6vzsv38001@xxxxxxxxxxxxxx>
Date: Sat, 02 Feb 2002 15:27:46 +0100
Salve,
riprendendo un filone discusso a suo tempo in lista [1], riporto i tempi dei soliti hdparm -Tt per il kernel 2.2.17 e per il kernel 2.4.9,
in entrambi i casi patchati RedHat. L'host è un Athlon 700 con chipset
VIA (quello con problemi di DMA), un controller SCSI Tekram DC-390UW
da 80 MB/s e i dischi SCSI sono 18GB 10000 rpm.

kernel 2.2.17:

/dev/hda:
 Timing buffer-cache reads:   128 MB in  0.77 seconds =166.23 MB/sec
 Timing buffered disk reads:  64 MB in  7.82 seconds =  8.18 MB/sec

/dev/sda:
 Timing buffer-cache reads:   128 MB in  0.80 seconds =160.00 MB/sec
 Timing buffered disk reads:  64 MB in  2.59 seconds = 24.71 MB/sec

/dev/sdb:
 Timing buffer-cache reads:   128 MB in  0.80 seconds =160.00 MB/sec
 Timing buffered disk reads:  64 MB in  2.57 seconds = 24.90 MB/sec

/dev/md5:
 Timing buffer-cache reads:   128 MB in  0.72 seconds =177.78 MB/sec
 Timing buffered disk reads:  64 MB in  1.51 seconds = 42.38 MB/sec

/dev/md4:
 Timing buffer-cache reads:   128 MB in  0.67 seconds =191.04 MB/sec
 Timing buffered disk reads:  64 MB in  1.42 seconds = 45.07 MB/sec

/dev/md3:
 Timing buffer-cache reads:   128 MB in  0.70 seconds =182.86 MB/sec
 Timing buffered disk reads:  64 MB in  1.70 seconds = 37.65 MB/sec

/dev/md2:
 Timing buffer-cache reads:   128 MB in  0.70 seconds =182.86 MB/sec
 Timing buffered disk reads:  64 MB in  2.95 seconds = 21.69 MB/sec

/dev/md1:
 Timing buffer-cache reads:   128 MB in  0.68 seconds =188.24 MB/sec
 Timing buffered disk reads:  64 MB in  1.30 seconds = 49.23 MB/sec

/dev/md0:
 Timing buffer-cache reads:   128 MB in  0.72 seconds =177.78 MB/sec
 Timing buffered disk reads:  64 MB in  1.71 seconds = 37.43 MB/sec

kernel 2.4.9:


/dev/hda:
 Timing buffer-cache reads:   128 MB in  0.69 seconds =185.51 MB/sec
 Timing buffered disk reads:  64 MB in  7.86 seconds =  8.14 MB/sec

/dev/sda:
 Timing buffer-cache reads:   128 MB in  0.69 seconds =185.51 MB/sec
 Timing buffered disk reads:  64 MB in  2.61 seconds = 24.52 MB/sec

/dev/sdb:
 Timing buffer-cache reads:   128 MB in  0.70 seconds =182.86 MB/sec
 Timing buffered disk reads:  64 MB in  2.61 seconds = 24.52 MB/sec

/dev/md5:
 Timing buffer-cache reads:   128 MB in  0.67 seconds =191.04 MB/sec
 Timing buffered disk reads:  64 MB in  1.53 seconds = 41.83 MB/sec

/dev/md4:
 Timing buffer-cache reads:   128 MB in  0.67 seconds =191.04 MB/sec
 Timing buffered disk reads:  64 MB in  1.43 seconds = 44.76 MB/sec

/dev/md3:
 Timing buffer-cache reads:   128 MB in  0.70 seconds =182.86 MB/sec
 Timing buffered disk reads:  64 MB in  1.39 seconds = 46.04 MB/sec

/dev/md2:
 Timing buffer-cache reads:   128 MB in  0.68 seconds =188.24 MB/sec
 Timing buffered disk reads:  64 MB in  2.72 seconds = 23.53 MB/sec

/dev/md1:
 Timing buffer-cache reads:   128 MB in  0.66 seconds =193.94 MB/sec
 Timing buffered disk reads:  64 MB in  1.32 seconds = 48.48 MB/sec

/dev/md0:
 Timing buffer-cache reads:   128 MB in  0.70 seconds =182.86 MB/sec
 Timing buffered disk reads:  64 MB in  1.33 seconds = 48.12 MB/sec

Le cose che noto io sono:
- l'accesso al disco sembra peggiorato nel 2.4.9, seppur di poco;
- l'accesso alla cache mostra un deciso miglioramento;
- il RAID 0 su due dischi SCSI porta quasi al raddoppio delle
  prestazioni di lettura da disco;
- il RAID 1 su due dischi SCSI ha circa le stesse prestazioni in
  lettura di un disco solo, quindi non viene affatto sfruttata la
  possibilità di interleaving ... non so se si tratta di un artefatto
  di hdparm o che altro.

Davide Bolcioni
--
There is no place like /home.



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