RFR: Caching MethodType's descriptor string improves lambda linkage performance

Sergey Kuksenko sergey.kuksenko at oracle.com
Tue Sep 17 11:19:00 PDT 2013

On 09/17/2013 04:41 AM, John Rose wrote:
> The algorithmic change (string cache) is acceptable, although it will tend to increase footprint somewhat.  
I don't think that it would be visible footprint increasing. MethodTypes
are interned by implementation, so I don't expect that this "overhead"
will be significant.

> We can tweak that later if necessary.  There are probably only a small number of such strings, so maybe a small leaky map would do the trick as well. 
In case of small amount of such strings we will get a huge overhead from
any kind of map. From performance point of view map may acceptable when
we have a lot of such strings. The key fact here that we have a few
amount of MethodTypes, but calls "toMethodDescriptorString@ very frequent.

> But, please don't hand-inline methods (checkPtype, checkSlotCount).  That is usually the wrong answer.  
> If there is a JIT inlining decision that isn't going right, we need to fix that, not distort the Java code.
Unfortunately it is not a case when we may rely on JIT. Certainly, there
are no perf problems here (except caching) after JIT (at least C2, I did
n't check C1). But we have huge performance problems/impact here while
interpreting. I know (I think) a really general solution for such perf
problems. Besides it will be useful in a big amount of other places.  It
is a bytecode level inline before interpretation.

Let's back to the patch.

checkPType is method which performs two _different_ actions. The first
is check that type in not null and type is not void. The second action
is calculate size of extra parameter slot (lond/double types). So we
came to idea that we need two different methods as from performance and
OOP purity points of view. checkPType has exactly two usages. And the
second usage don't need calculate size of parameters slots. So one
action used only in the single place and we get more readable code if we
inline it. The second action used twice, but it a very simple action
(NPE and void check) and I think here we may do manual inline because of
it is give us visible benefits and don't create any problems as for
later JITing and code reading.

> Also, I think you deleted a call to checkSlotCount that should still be there to detect illegal inputs.  One of the costs of hand-inlining is bitrot like that.
You are right. I did a mistake. I eliminate one checkSlotCount usage by
error, but I didn't inline anything in that place. So it is not a cost
of hand-inlining, it is a cost of my inadvertence when I eliminame a
whole code line by misclick and didn't noticed that.

Tomorrow I'll do other webrev -  will try to pay attention to all
comments and we may continue the discussion.

> — John
> On Sep 11, 2013, at 12:03 PM, Sergey Kuksenko <sergey.kuksenko at oracle.com> wrote:
>> On 09/11/2013 09:01 PM, Aleksey Shipilev wrote:
>>> On 09/11/2013 08:23 PM, Sergey Kuksenko wrote:
>>>> http://cr.openjdk.java.net/~skuksenko/jsr335/8024635/webrev.00/
>>> As much as I hate to see the hand code tweaking instead of relying on
>>> compiler to do it's job, I understand this is about interpreter. Seems
>>> good then.
>>> * Formatting: "if(...)" should be "if (...")
>> Will do
>>> * Formatting: "//NPE" should be "// null check"
>> I just preserve exiting comments.
>> Decided don't modify original code which is not important to required
>> functionality.
>>> * Formatting: "desc =  " should be "desc = "
>>> * Formatting: this one should not use braces (for consistency with other
>>> usages)?
>>> 364         if(nptype == null) { //NPE
>>> 365             throw new NullPointerException();
>>> 366         }
>> Let ask code owner.
>>> * Explicit null-checks: implicits via .getClass and .equals always
>>> bothered me in j.l.i.*; the idea was seemingly to piggyback on the
>>> compiler intrinsics. 
>> anyway it is doesn't matter after C1/C2
>>> Any idea what's the cost of using
>>> Objects.requireNonNull there?
>> If we are running under the interpreter Objects.requireNonNull costs
>> enough to eliminate benefits from this fine tuning.
>> -- 
>> Best regards,
>> Sergey Kuksenko

Best regards,
Sergey Kuksenko

More information about the hotspot-compiler-dev mailing list