terminology - What is voluntary preemption? -

-

what voluntary preemption? know it's concept in scheduling.

it depends little bit on os.

in rtos, voluntary preemption means running process declares points can preempted (where otherwise run until completion). way think of variant of yield in coroutine. in contrast desktop os kernel determines preemption. keep in mind rtos not have concept of "user mode".

in linux (at least), "voluntary preemption" bit of misnomer:

traditionally (no forced preemption), when user process making system call (in kernel mode), block until completion. user mode code preempted.

the preemptive kernel such kernel code can preempted. sounds redundant it's worth noting mean kernel preemptible, not "the kernel supports preemption". forced/involuntary preemption means while servicing system call, interrupt high priority user process can "force" kernel context switch run (technically it's not context switch, has same effect). decreases latency of user process "seeing" change in hardware state.

voluntary preemption kernel periodically checks see if should reschedule processes "while doing kernel things". is, instead of scheduling/rescheduling user processes @ preemption points, periodically while handling things such i/o. so, high priority user process might still have wait low priority process finish slice, high prioirty process might run "early" kernel checking more if it's run. decreases latency of user process moving suspended state running state (at expense of overall system throughput).


Comments

Post a Comment

Popular posts from this blog

c# - How to set Z index when using WPF DrawingContext? -

-
how set z-index drawing object when using drawingcontext.drawxxx() methods? the object drawn last have higher z index. can't change index of drawn objects. way draw in order. if using wpf (as placed tag), can use, example, canvas control. create shapes need like polyline obj = new polyline(); //... // ... set properties of obj and add them canvas uielementcollection: yourcanvasname.children.add(obj); //or yourcanvasname.children.insert(i, obj); first items of collection have higher z index. advantages in way: no need redraw on window changes, can anytime move objects , change order.
Read more

razor - Is this a bug in WebMatrix PageData? -

-
i think may have found bug in webmatrix's pagedata, not sure. concerns how pass data partial page calling page. in webmatrix documentation (tutorials, e.g. " 3 - creating consistent look ", , example code), pagedata recommended mechanism pass data between pages (e.g. content page layout page, or partial page). however have found not work other way, pass data partial page calling page. modifying or adding entries in pagedata in partial page, not seem calling page. cutting right down simplest possible example, in test page may have this: @{ pagedata["test"] = "initial entry"; } <p>before calling partial page, test value @pagedata["test"]</p> @renderpage("_testpartial.cshtml") <p>after returning calling page, test value @pagedata["test"]</p> and in _testpartial.cshtml page might have this: @{ pagedata["test"] = "modified entry"; } <p>in partial page...
Read more

visual c++ - Using relative values in array sorting ( asm ) -

-
i need sort through array , sort each individual row in array in ascending order. doesn't seem going (surprise!) keep getting hit 2 errors: a2101: cannot add 2 relocatable labels , a2026: constant expected here's sort, makes sense me, think i'm still trying implement high-lvl language techniqes assembly. there way around not being able use relative values? (the array 7 rows 9 columns, btw). mov cx, 7; cx = number of rows outer: ; outer loop walk through rows push cx mov cx, 9 mov row, cx ;rows middle: ; middle-loop walk through columns push cx sub cx, 1 ;cx = cx-1 mov column, cx ;columns inner: ;inner loop - compare , exchange column values cmp marray[row*9 + column], marray[row*9 + column+1] xchg marray[row*9 + column+1], marray[row*9 + column] ; compare , exchange values marray table inc column loop inner pop cx loop mid...
Read more