Hardware Reference
In-Depth Information
Pitfall Ignoring The Impact Of The Operating System On The Performance Of The
Memory Hierarchy.
Figure B.29 shows the memory stall time due to the operating system spent on three large
workloads. About 25% of the stall time is either spent in misses in the operating system or res-
ults from misses in the application programs because of interference with the operating sys-
tem.
FIGURE B.29 Misses and time spent in misses for applications and operating system .
The operating system adds about 25% to the execution time of the application. Each pro-
cessor has a 64 KB instruction cache and a two-level data cache with 64 KB in the first level
and 256 KB in the second level; all caches are direct mapped with 16-byte blocks. Collected
on Silicon Graphics POWER station 4D/340, a multiprocessor with four 33 MHz R3000 pro-
cessors running three application workloads under a UNIX System V—Pmake, a parallel com-
pile of 56 files; Multipgm, the parallel numeric program MP3D running concurrently with
Pmake and a five-screen edit session; and Oracle, running a restricted version of the TP-1
benchmark using the Oracle database. (Data from Torrellas, Gupta, and Hennessy [1992].)
Pitfall Relying On The Operating Systems To Change The Page Size Over Time.
The Alpha architects had an elaborate plan to grow the architecture over time by growing its
page size, even building it into the size of its virtual address. When it came time to grow page
sizes with later Alphas, the operating system designers balked and the virtual memory system
was revised to grow the address space while maintaining the 8 KB page.
Architects of other computers noticed very high TLB miss rates, and so added multiple, lar-
ger page sizes to the TLB. The hope was that operating systems programmers would allocate
an object to the largest page that made sense, thereby preserving TLB entries. After a decade of
trying, most operating systems use these “superpages” only for handpicked functions: map-
ping the display memory or other I/O devices, or using very large pages for the database code.
 
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