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Date: Sat, 15 Apr 1995 14:04:59 -0700
From: Bruce Evans <bde>
Message-Id: <199504152104.OAA00998@freefall.cdrom.com>
To: CVS-commiters, cvs-sys
Subject: cvs commit: src/sys/kern tty.c
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bde         95/04/15 14:04:59

  Modified:    sys/kern tty.c
  Log:
  Speed up ttnread() in the !(ICANON | ISIG) case by copying to user space
  through a temporary buffer instead of one character at a time.  The old
  method takes about 6 usec/char on a 486DX2/66.  This is larger than than
  the combined interrupt and PIO overhead for a 16550!
  
  This change was first implemented in 1.1.5.  It was rewritten for 2.1.
  The clist access functions allow a simpler implementation at some cost
  in correctness and speed.  There needs to be an ungetc() function to
  recover from EFAULT, and it wastes time to copy through a temporary
  buffer.
  
  Don't snoop on single characters that weren't read due to EFAULT.
  Rewrite a snoop comment in my approximation to English.
  
  Undo bogus exportation of ttnread().