The following sequence
int fd = open(argv[1], O_RDWR | O_CREAT | O_DIRECT, 0644);
for (i = 0; i < 100000; i++)
write(fd, buf, 4096);
performs 10% better if buf is aligned to 4096 bytes rather then to
512 bytes on HDD with 512/4096 logical/physical sector size.
The difference is quite reliable.
I have used the following program to test
#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <malloc.h>
#include <string.h>
int main(int argc, char *argv[])
{
int fd = open(argv[1], O_RDWR | O_CREAT | O_DIRECT, 0644);
void *buf;
int i = 0;
do {
buf = memalign(512, 4096); <--- replace 512 with 4096
if ((unsigned long)buf & 4095)
break;
i++;
} while (1);
printf("%d\n", i);
memset(buf, 0x11, 4096);
for (i = 0; i < 100000; i++)
write(fd, buf, 4096);
close(fd);
return 0;
}
time for in in `seq 1 30` ; do a.out aa ; done
The file was placed into 8 GB partition on HDD below to avoid speed
change due to different offset on disk. Results are reliable:
- 189 vs 180 seconds on Linux 3.16
Signed-off-by: Denis V. Lunev <d...@openvz.org>
CC: Kevin Wolf <kw...@redhat.com>
CC: Stefan Hajnoczi <stefa...@redhat.com>
hades ~/src/qemu # hdparm -I /dev/sdg
/dev/sdg:
ATA device, with non-removable media
Model Number: WDC WD20EZRX-07D8PB0
Serial Number: WD-WCC4M5LVSAEP
Firmware Revision: 80.00A80
Transport: Serial, SATA 1.0a, SATA II Extensions, SATA Rev 2.5,
SATA Rev 2.6, SATA Rev 3.0
Standards:
Supported: 9 8 7 6 5
Likely used: 9
Configuration:
Logical max current
cylinders 16383 16383
heads 16 16
sectors/track 63 63
--
CHS current addressable sectors: 16514064
LBA user addressable sectors: 268435455
LBA48 user addressable sectors: 3907029168
Logical Sector size: 512 bytes
Physical Sector size: 4096 bytes
device size with M = 1024*1024: 1907729 MBytes
device size with M = 1000*1000: 2000398 MBytes (2000 GB)
cache/buffer size = unknown
Nominal Media Rotation Rate: 5400
Capabilities:
LBA, IORDY(can be disabled)
Queue depth: 32
Standby timer values: spec'd by Standard, with device specific minimum
R/W multiple sector transfer: Max = 16 Current = 16
DMA: mdma0 mdma1 mdma2 udma0 udma1 udma2 udma3 udma4 udma5 *udma6
Cycle time: min=120ns recommended=120ns
PIO: pio0 pio1 pio2 pio3 pio4
Cycle time: no flow control=120ns IORDY flow control=120ns
Commands/features:
Enabled Supported:
* SMART feature set
Security Mode feature set
* Power Management feature set
* Write cache
* Look-ahead
* Host Protected Area feature set
* WRITE_BUFFER command
* READ_BUFFER command
* NOP cmd
* DOWNLOAD_MICROCODE
Power-Up In Standby feature set
* SET_FEATURES required to spinup after power up
SET_MAX security extension
* 48-bit Address feature set
* Device Configuration Overlay feature set
* Mandatory FLUSH_CACHE
* FLUSH_CACHE_EXT
* SMART error logging
* SMART self-test
* General Purpose Logging feature set
* 64-bit World wide name
* WRITE_UNCORRECTABLE_EXT command
* {READ,WRITE}_DMA_EXT_GPL commands
* Segmented DOWNLOAD_MICROCODE
* Gen1 signaling speed (1.5Gb/s)
* Gen2 signaling speed (3.0Gb/s)
* Gen3 signaling speed (6.0Gb/s)
* Native Command Queueing (NCQ)
* Host-initiated interface power management
* Phy event counters
* NCQ priority information
* READ_LOG_DMA_EXT equivalent to READ_LOG_EXT
* DMA Setup Auto-Activate optimization
Device-initiated interface power management
* Software settings preservation
* SMART Command Transport (SCT) feature set
* SCT Write Same (AC2)
* SCT Features Control (AC4)
* SCT Data Tables (AC5)
unknown 206[12] (vendor specific)
unknown 206[13] (vendor specific)
unknown 206[14] (vendor specific)
Security:
Master password revision code = 65534
supported
not enabled
not locked
frozen
not expired: security count
supported: enhanced erase
276min for SECURITY ERASE UNIT. 276min for ENHANCED SECURITY ERASE UNIT.
Logical Unit WWN Device Identifier: 50014ee2b5da838c
NAA : 5
IEEE OUI : 0014ee
Unique ID : 2b5da838c
Checksum: correct
hades ~/src/qemu #
