Content-type: text/html Man page of sys_attrs_io

sys_attrs_io

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NAME

sys_attrs_io - io subsystem attributes  

DESCRIPTION

This reference page lists and describes attributes for the I/O (io) kernel subsystem. Refer to the sys_attrs(5) reference page for an introduction to the topic of kernel subsystem attributes.

Amount of space in megabytes to allocate for the 32-bit scatter-gather DMA window on PCI-based AlphaServers. This parameter is set by the TruCluster software.
Default value: 0 (MB)
Do not modify the value of this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
Number of entry dispatch points supported by the in-memory table for the bdev (block device driver) switch. This table is used to access block device drivers, and must be large enough to accommodate the drivers registered in the bdevsw table in the /usr/sys/system_name /conf.c file, plus any additional device drivers that will be dynamically loaded.
Default value: 140
Minimum value: 0
Maximum value: INT_MAX
If the number of third-party block device drivers that will be dynamically loaded to the system plus the number of block device drivers already registered in the system_name /conf.c file exceeds 140, you may want to increase the value of bdevsw_size.
Number of buffers either added to or removed from the buffer pool free list. Buffers are allocated as they are needed in order to handle immediate demands; however, they are deallocated carefully to prevent spikes.
Default value: 50 buffers
Do not modify the default setting for this attribute unless instructed to do so by Compaq support personnel or by patch kit instructions.
A threshold value that determines when more buffers are allocated from the kernel. More buffers are allocated from the kernel when the number of buffers in the pool free list falls below this value. CAM reserves the number of buffers specified by the cam_ccb_low_water attribute to ensure that the kernel always has enough memory to shut down runaway processes.
Default value: 100 (buffers)
Do not modify the default setting for this attribute unless instructed to do so by Compaq support personnel or by patch kit instructions.
The base number of Common Access Method (CAM) control blocks (ccbs) allocated to the buffer pool free list. One ccb is needed for each outstanding I/O request. The system will automatically increase the number of ccbs, as necessary for the I/O load, but will not decrease allocation of ccbs below cam_ccb_pool_size.
Default value: 200 (ccbs)
Minimum value: 100
Maximum value: 1000
If the I/O load on your system is consistently very high, increasing the number of ccbs that are always available in memory (rather than starting with a lower number and letting the system dynamically increase it when necessary) may improve performance. However, by increasing cam_ccb_pool_size, you prevent the system from using the additional memory for other purposes at times when the number of I/O requests is lower than the number of ccbs. Any performance improvement that results from a cam_ccb_pool_size increase can occur only if your system's memory size is large enough to support the dedication of additional memory resources to I/O.
Decreasing cam_ccb_pool_size to a value below the default is very likely to cause I/O problems and is strongly discouraged.
Number of entry dispatch points supported by the in-memory table for the cdev (character device driver) switch. This table is used to access character device drivers, and must be large enough to accommodate the drivers registered in the cdevsw table in the /usr/sys/system_name /conf.c file, plus any additional character device drivers that will be dynamically loaded.
Default value: 125 (entry dispatch points)
Minimum value: 0
Maximum value: INT_MAX
If the number of third-party character device drivers that will be dynamically loaded to the system plus the number of character device drivers already registered in the system_name /conf.c file exceeds 125, you may want to increase the value of cdevsw_size.
An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by Compaq support personnel or by patch kit instructions.
An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by Compaq support personnel or by patch kit instructions.
An on/off switch for internal use only. Do not modify this attribute unless instructed to do so by Compaq support personnel or by patch kit instructions. Default value: 0
Do not modify the default value of this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation. Amount of space in megabytes to allocate for the 64-bit scatter-gather DMA window on PCI-based AlphaServers.
Default value: 0 (MB)
Do not modify this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation. A value that controls the zeroing of scatter-gather mapping entries in the PCI adapter on AS8x00 Alphaservers.
Default value: 2
Do not modify this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
The size, in bytes, of an I/O read request used by nondriver kernel code if an ioctl() call fails or returns 0 (zero). (When nondriver kernel code needs to know the maximum size of an I/O read request for a block-I/O device, it issues an ioctl call to the driver.)
Default value: 65536 (bytes)
Change the default value of this attribute only if a third-party device driver does not use the ioctl call and has a maximum size that is less than the default value (65536 bytes, or 64 kilobytes) in the sysconfigtab file . (The person writing the third-party device driver must provide information, either in documentation or an installation script, on how to change the entry in the sysconfigtab file to the correct value.)
The size, in bytes, of an I/O write request used by nondriver kernel code if an ioctl() call fails or returns 0 (zero). (When nondriver kernel code needs to know the maximum size of an I/O write request for a block-I/O device, it issues an ioctl() call to the driver.)
Default value: 65536 (bytes)
Change the default value of this attribute only if a third-party device driver does not use the ioctl call and has a maximum size that is less than the default value (64 KB) in the sysconfigtab file. (The person writing the third-party device driver must provide information, either in documentation or an installation script, on how to change the entry in the sysconfigtab file to the correct value.) Default value: 0
Do not modify the default setting of this attribute unless instructed to do so by Compaq Computer Corporation support personnel or by patch kit documentation.
 

SEE ALSO

sys_attrs(5)


 

Index

NAME
DESCRIPTION
SEE ALSO

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Time: 02:43:09 GMT, October 02, 2010