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authorChris Metcalf <cmetcalf@tilera.com>2011-02-28 13:21:52 -0500
committerChris Metcalf <cmetcalf@tilera.com>2011-03-01 16:20:04 -0500
commit13371731487896a6ef158b1cd74297f40a3da4bb (patch)
treeaf09fca3fd8811340b373faaddcdb528f8a07669 /arch/tile/include/hv
parent04f7a3f12e10032ee3d44df1a509dbf5b2001fce (diff)
downloadop-kernel-dev-13371731487896a6ef158b1cd74297f40a3da4bb.zip
op-kernel-dev-13371731487896a6ef158b1cd74297f40a3da4bb.tar.gz
arch/tile: fix __ndelay etc to work better
The current implementations of __ndelay and __udelay call a hypervisor service to delay, but the hypervisor service isn't actually implemented very well, and the consensus is that Linux should handle figuring this out natively and not use a hypervisor service. By converting nanoseconds to cycles, and then spinning until the cycle counter reaches the desired cycle, we get several benefits: first, we are sensitive to the actual clock speed; second, we use less power by issuing a slow SPR read once every six cycles while we delay; and third, we properly handle the case of an interrupt by exiting at the target time rather than after some number of cycles. Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Diffstat (limited to 'arch/tile/include/hv')
-rw-r--r--arch/tile/include/hv/hypervisor.h5
1 files changed, 5 insertions, 0 deletions
diff --git a/arch/tile/include/hv/hypervisor.h b/arch/tile/include/hv/hypervisor.h
index f672544..103986b 100644
--- a/arch/tile/include/hv/hypervisor.h
+++ b/arch/tile/include/hv/hypervisor.h
@@ -964,6 +964,11 @@ HV_ASIDRange hv_inquire_asid(int idx);
/** Waits for at least the specified number of nanoseconds then returns.
*
+ * NOTE: this deprecated function currently assumes a 750 MHz clock,
+ * and is thus not generally suitable for use. New code should call
+ * hv_sysconf(HV_SYSCONF_CPU_SPEED), compute a cycle count to wait for,
+ * and delay by looping while checking the cycle counter SPR.
+ *
* @param nanosecs The number of nanoseconds to sleep.
*/
void hv_nanosleep(int nanosecs);
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