-qtune

Pragma equivalent

None.

Purpose

Tunes instruction selection, scheduling, and other architecture-dependent performance enhancements to run best on a specific hardware architecture. Allows specification of a target SMT mode to direct optimizations for best performance in that mode.

Syntax


                 .-balanced-.                        
>>- -q--tune--=--+-auto-----+--+-----------------+-------------><
                 +-ppc970---+  |    .-st-------. |   
                 +-pwr4-----+  '-:--+-balanced-+-'   
                 +-pwr5-----+       +-smt2-----+     
                 +-pwr6-----+       +-smt4-----+     
                 +-pwr7-----+       '-smt8-----'     
                 '-pwr8-----'

Defaults

-qtune=balanced:balanced when no valid -qarch setting is in effect. Otherwise, the default depends on the effective -qarch setting. For details, see Table 1.

Parameters for CPU suboptions

The following CPU suboptions allow you to specify a particular architecture for the compiler to target for best performance:

auto: Optimizations are tuned for the platform on which the application is compiled.
balanced: Optimizations are tuned across a selected range of recent hardware.
ppc970: Optimizations are tuned for the PowerPC® 970 processor.
pwr4: Optimizations are tuned for the POWER4 hardware platforms.
pwr5: Optimizations are tuned for the POWER5 hardware platforms.
pwr6: Optimizations are tuned for the POWER6® hardware platforms.
pwr7: Optimizations are tuned for the POWER7® or POWER7+™ hardware platforms.
pwr8: Optimizations are tuned for the POWER8® hardware platforms.

Parameters for SMT suboptions

The following simultaneous multithreading (SMT) suboptions allow you to optionally specify an execution mode for the compiler to target for best performance.

balanced: Optimizations are tuned for performance across various SMT modes for a selected range of recent hardware.
st: Optimizations are tuned for single-threaded execution.
smt2: Optimizations are tuned for SMT2 execution mode (two threads).
smt4: Optimizations are tuned for SMT4 execution mode (four threads).
smt8: Optimizations are tuned for SMT8 execution mode (eight threads).

Usage

If you want your program to run on more than one architecture, but to be tuned to a particular architecture, you can use a combination of the -qarch and -qtune options. These options are primarily of benefit for floating-point intensive programs.

By arranging (scheduling) the generated machine instructions to take maximum advantage of hardware features such as cache size and pipelining, -qtune can improve performance. It only has an effect when used in combination with options that enable optimization.

A particular SMT suboption is valid if the effective -qarch option supports the specified SMT mode. The acceptable combinations of the -qarch and SMT tune options are listed in Table 1. The compiler ignores any invalid -qarch/-qtune SMT combination.

Although changing the -qtune setting may affect the performance of the resulting executable, it has no effect on whether the executable can be executed correctly on a particular hardware platform.

Acceptable combinations of -qarch and -qtune are shown in the following table.

Table 1. Acceptable -qarch/-qtune combinations
-qarch option	Default -qtune setting	Available -qtune CPU settings	Available -qtune SMT settings
ppc	balanced:balanced	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
ppcgr	balanced:balanced	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
ppc64	balanced:balanced	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
ppc64gr	balanced:balanced	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
ppc64grsq	balanced:balanced	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
ppc64v	balanced:balanced	auto \| ppc970 \| pwr6 \| pwr7 \| pwr8 \| balanced	balanced \| st
ppc970	ppc970:st	auto \| ppc970 \| balanced	balanced \| st
pwr4	pwr4:st	auto \| pwr4 \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| ppc970 \| balanced	balanced \| st
pwr5	pwr5:st	auto \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| balanced	balanced \| st
pwr5x	pwr5:st	auto \| pwr5 \| pwr6 \| pwr7 \| pwr8 \| balanced	balanced \| st \| smt2
pwr6	pwr6:st	auto \| pwr6 \| pwr7 \| pwr8 \| balanced	balanced \| st \| smt2
pwr6e	pwr6:st	auto \| pwr6 \| balanced	balanced \| st
pwr7	pwr7:st	auto \| pwr7 \| pwr8 \| balanced	balanced \| st \| smt2 \| smt4
pwr8	pwr8:st	auto \| pwr8 \| balanced	balanced \| st \| smt2 \| smt4 \| smt8

Predefined macros