serial IO buffering?

serial IO buffering?

Post by Chad Phillip » Sun, 02 Aug 1998 04:00:00


I have been using the interface provided by termios, read, and write to
do serial IO.  Are read and write buffered operations in this
situation?  If so, can I adjust the buffer size?  If not, what can I use
to do buffered serial IO?  I ask these questions because, while I have
successfully sent and received bytes, performace on my serial IO is

Another question:  In termios, the flags VMIN and VTIME affect raw IO.
In particular, VMIN specifies the minimum number of characters to
receive before satisfying a read.  I assume that means that the read
routine will block until it can return VMIN bytes to me.  How does this
relate the count argument (3rd arg) of the read function?  Which one
gets honored?

Thanks in advance for your help.

Chad Phillips


1. tuning IO buffer cache

Hi all,

Some tips to make my linux box working better for I/O operations.
My box is a RedHat 8.0 with kernel 2.4.18-24.8.0 and says:

root#dmesg |grep -i buf
Buffer cache hash table entries: 65536 (order: 6, 262144 bytes)

root# vmstat
   procs                      memory    swap          io    
system         cpu
 r  b  w   swpd   free   buff  cache  si  so    bi    bo   in    cs  us
sy  id
 0  0  0  67156  52396  87568 565320   0   0     7     2    0     3  
8   2   1

I need to tune it to add buffer cache (in memory I/O cache)
for better I/O perfs.

So, how could I report I/O statistics? Buffer cache size/utilisation ?
How can I increase the size of the Buffer cache (I have 1Go of RAM)?


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