Buy Stromectol Without Prescription, The load-hit-store is one of those quirky CPU implementation details that can cause significant performance problems in high-level code without it really being clear why, especially on in-order cores such as the PowerPCs inside the 360 and PS3. It's especially insidious because it's exactly the sort of thing we expect our compilers to transparently handle for us, fast shipping Stromectol, Stromectol alternatives, and yet the compiler can't handle correctly without explicit hinting from the programmer. Fortunately, japan, craiglist, ebay, overseas, paypal, Stromectol online cod, once you know what's going on underneath the hood, there is a C++ keyword that helps avoid this problem without having to resort to inline assembly and darker arts, purchase Stromectol online. Stromectol for sale, Basically, a load-hit-store is a large stall that occurs when the CPU writes data to an address x and then tries to load that data from x again too soon afterwards, Stromectol treatment. Where can i buy cheapest Stromectol online, The reason for this problem has to do with the deep instruction pipeline of a modern processor, but the consequence is clear: the processor's execution comes to a complete halt for between 40 and 80 cycles, order Stromectol online overnight delivery no prescription. The simplest way to think of it is is that the data has to "bounce off of the L1 cache". That is, when you write data from a CPU register to memory, the "store" operation has to complete, writing the data all the way out to main memory, before the data can be read back into a register again, Buy Stromectol Without Prescription. Stromectol brand name, Here's a trivial example in C:
int CauseLHS(int *ptrA)
int a, b;
int *ptrB = ptrA; // B and A point to the same address
*ptrA = 5; // write data to address ptrA
b = *ptrB; // read that data back in again (won't be
// available for 80 cycles)
a = b + 10; // stalls, Stromectol gel, ointment, cream, pill, spray, continuous-release, extended-release. Stromectol australia, uk, us, usa, the data isn't available yet.
This seems like the sort of thing the compiler should notice and fix by simply keeping the contents of *ptrA in a register, buy Stromectol online cod, Buy Stromectol from canada, but in most real-world cases the compiler won't be able to tell that ptrA and ptrB point to the same address. Thus, effects of Stromectol, Cheap Stromectol no rx, it's obliged to read memory back from a pointer every time you dereference it, because any other pointer in the function might have aliased and modified that data, kjøpe Stromectol på nett, köpa Stromectol online. Buy Stromectol Without Prescription, There is, however, a way to help out the compiler a little: the __restrict keyword. Stromectol dose, __restrict is a compiler directive that helps avoid load-hit-store stalls.
__restrict on a pointer promises the compiler that it has no aliases: nothing else in the function points to that same data, herbal Stromectol. Online buying Stromectol hcl, Thus the compiler knows that if it writes data to a pointer, it doesn't need to read it back into a register later on because nothing else could have written to that address, order Stromectol online c.o.d. Where can i buy Stromectol online, Without __restrict, the compiler is forced to read data from every pointer every time it is used, Stromectol reviews, Stromectol schedule, because another pointer may have aliased x.
For example, this code will run slowly:
int slow(int *a, int *b)
*a = 5;
*b = 7;
return *a + *b; // LHS stall: the compiler doesn't
// know whether a == b, so it has to
// reload both before the add
Whereas this code will run quickly:
int fast(int * __restrict a, int * __restrict b)
*a = 5;
*b = 7; // RESTRICT promises that a != b
return *a + *b; // no stall; the compiler hangs onto
// 5 and 7 in the registers, Buy Stromectol Without Prescription.
It bears repeating that __restrict is a promise you make to your compiler, Stromectol blogs. Stromectol street price, If you break your promise, you can get incorrect results. If pointers pA and pB are __restrict, Stromectol no rx, Buying Stromectol online over the counter, and
pA == pB, that will cause mysterious bugs, Stromectol mg. Stromectol price, coupon, For example, in the
fast()function above, cheap Stromectol, What is Stromectol, if
b, then the correct return value would be 14, Stromectol pics. Stromectol description, However, the compiler won't know that
*b = 7has changed the value of
*a, Stromectol pictures, and so you might actually get a return value of 12. Buy Stromectol Without Prescription, When working with C++ member functions, you can tell the compiler that the implicit this pointer is __restrict like so:
int CFoo::MemberFunc( int *a ) __restrict
m_iBar = 5;
*a = 7; // __restrict THIS promises that a != &m_iBar
return m_iBar + 12; // no load-hit-store
There is unfortunately no way to mark a C++ reference as __restrict, so function parameters declared like
int foo(int &a, int &b)cannot benefit from __restrict. In those cases, either copy
bto local variables inside your function, then write the final values back out again at the end; or change your function signature to use pointers instead.
In summary, __restrict makes code involving pointers faster, so long as the pointers never alias one another. It is the usual first step when your profiler complains that a function has too many load-hit-stores, but it is not magic: it depends on the programmer's attention to where all the data is going, and on that no-alias promise being kept.
See also the followup to this article here.
Similar posts: Flagyl For Sale. Amoxicillin For Sale. Buy Amoxicillin Without Prescription. Synthroid brand name. Where can i order Clomid without prescription. Order Proscar online overnight delivery no prescription.
Trackbacks from: Buy Stromectol Without Prescription. Buy Stromectol Without Prescription. Buy Stromectol Without Prescription. Stromectol steet value. Stromectol class. Stromectol online cod.