From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow path Date: Tue, 16 Jul 2019 17:58:39 +0200 Message-ID: <20190716155839.GF3402@hirez.programming.kicks-ass.net> References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-3-alex.kogan@oracle.com> <20190716102034.GN3419@hirez.programming.kicks-ass.net> <9D5B6F33-6003-4CCA-BBE5-998B5A679B9C@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: base64 Return-path: Content-Disposition: inline In-Reply-To: <9D5B6F33-6003-4CCA-BBE5-998B5A679B9C@oracle.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Alex Kogan Cc: linux-arch@vger.kernel.org, guohanjun@huawei.com, arnd@arndb.de, dave.dice@oracle.com, jglauber@marvell.com, x86@kernel.org, will.deacon@arm.com, linux@armlinux.org.uk, steven.sistare@oracle.com, linux-kernel@vger.kernel.org, rahul.x.yadav@oracle.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, longman@redhat.com, tglx@linutronix.de, daniel.m.jordan@oracle.com, linux-arm-kernel@lists.infradead.org List-Id: linux-arch.vger.kernel.org T24gVHVlLCBKdWwgMTYsIDIwMTkgYXQgMTA6NTM6MDJBTSAtMDQwMCwgQWxleCBLb2dhbiB3cm90 ZToKPiBPbiBKdWwgMTYsIDIwMTksIGF0IDY6MjAgQU0sIFBldGVyIFppamxzdHJhIDxwZXRlcnpA aW5mcmFkZWFkLm9yZz4gd3JvdGU6Cj4gPiAKPiA+IE9uIE1vbiwgSnVsIDE1LCAyMDE5IGF0IDAz OjI1OjMzUE0gLTA0MDAsIEFsZXggS29nYW4gd3JvdGU6Cj4gPiAKPiA+PiArLyoKPiA+PiArICog c2V0X2xvY2tlZF9lbXB0eV9tY3MgLSBUcnkgdG8gc2V0IHRoZSBzcGlubG9jayB2YWx1ZSB0byBf UV9MT0NLRURfVkFMLAo+ID4+ICsgKiBhbmQgYnkgZG9pbmcgdGhhdCB1bmxvY2sgdGhlIE1DUyBs b2NrIHdoZW4gaXRzIHdhaXRpbmcgcXVldWUgaXMgZW1wdHkKPiA+PiArICogQGxvY2s6IFBvaW50 ZXIgdG8gcXVldWVkIHNwaW5sb2NrIHN0cnVjdHVyZQo+ID4+ICsgKiBAdmFsOiBDdXJyZW50IHZh bHVlIG9mIHRoZSBsb2NrCj4gPj4gKyAqIEBub2RlOiBQb2ludGVyIHRvIHRoZSBNQ1Mgbm9kZSBv ZiB0aGUgbG9jayBob2xkZXIKPiA+PiArICoKPiA+PiArICogKiwqLCogLT4gMCwwLDEKPiA+PiAr ICovCj4gPj4gK3N0YXRpYyBfX2Fsd2F5c19pbmxpbmUgYm9vbCBfX3NldF9sb2NrZWRfZW1wdHlf bWNzKHN0cnVjdCBxc3BpbmxvY2sgKmxvY2ssCj4gPj4gKwkJCQkJCSAgIHUzMiB2YWwsCj4gPj4g KwkJCQkJCSAgIHN0cnVjdCBtY3Nfc3BpbmxvY2sgKm5vZGUpCj4gPj4gK3sKPiA+PiArCXJldHVy biBhdG9taWNfdHJ5X2NtcHhjaGdfcmVsYXhlZCgmbG9jay0+dmFsLCAmdmFsLCBfUV9MT0NLRURf VkFMKTsKPiA+PiArfQo+ID4gCj4gPiBUaGF0IG5hbWUgaXMgbm9uc2Vuc2UuIEl0IHNob3VsZCBi ZSBzb21ldGhpbmcgbGlrZToKPiA+IAo+ID4gc3RhdGljIF9fYWx3YXlzX2lubGluZSBib29sIF9f dHJ5X2NsZWFyX3RhaWwo4oCmKQo+IAo+IFdlIGFscmVhZHkgaGF2ZSBzZXRfbG9ja2VkKCksIHNv IEkgd2FzIHRyeWluZyB0byBjb252ZXkgdGhlIGZhY3QgdGhhdCB3ZSBhcmUKPiBkb2luZyB0aGUg c2FtZSBoZXJlLCBidXQgb25seSB3aGVuIHRoZSBNQ1MgY2hhaW4gaXMgZW1wdHkuCj4gCj4gSSBj YW4gdXNlIF9fdHJ5X2NsZWFyX3RhaWwoKSBpbnN0ZWFkLgoKVGhpbmcgaXMsIHdlIGdvIGludG8g dGhpcyBmdW5jdGlvbiB3aXRoOiAqLDAsMSBhbmQgYXJlIHRyeWluZyB0byBvYnRhaW4KMCwwLDEu IElPVywgd2UncmUgdHJ5aW5nIHRvIGNsZWFyIHRoZSB0YWlsLCB3aGlsZSBwcmVzZXJ2aW5nIHBl bmRpbmcgYW5kCmxvY2tlZC4KCl9fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19f X19fX19fX19fCmxpbnV4LWFybS1rZXJuZWwgbWFpbGluZyBsaXN0CmxpbnV4LWFybS1rZXJuZWxA bGlzdHMuaW5mcmFkZWFkLm9yZwpodHRwOi8vbGlzdHMuaW5mcmFkZWFkLm9yZy9tYWlsbWFuL2xp c3RpbmZvL2xpbnV4LWFybS1rZXJuZWwK From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:33324 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732614AbfGPP66 (ORCPT ); Tue, 16 Jul 2019 11:58:58 -0400 Date: Tue, 16 Jul 2019 17:58:39 +0200 From: Peter Zijlstra Subject: Re: [PATCH v3 2/5] locking/qspinlock: Refactor the qspinlock slow path Message-ID: <20190716155839.GF3402@hirez.programming.kicks-ass.net> References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-3-alex.kogan@oracle.com> <20190716102034.GN3419@hirez.programming.kicks-ass.net> <9D5B6F33-6003-4CCA-BBE5-998B5A679B9C@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9D5B6F33-6003-4CCA-BBE5-998B5A679B9C@oracle.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Alex Kogan Cc: linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, longman@redhat.com, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com, jglauber@marvell.com, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com Message-ID: <20190716155839.w1FWEu2nHfIXvDeh1BLXt2xpELWcvA9SRXQwVACNR6Q@z> On Tue, Jul 16, 2019 at 10:53:02AM -0400, Alex Kogan wrote: > On Jul 16, 2019, at 6:20 AM, Peter Zijlstra wrote: > > > > On Mon, Jul 15, 2019 at 03:25:33PM -0400, Alex Kogan wrote: > > > >> +/* > >> + * set_locked_empty_mcs - Try to set the spinlock value to _Q_LOCKED_VAL, > >> + * and by doing that unlock the MCS lock when its waiting queue is empty > >> + * @lock: Pointer to queued spinlock structure > >> + * @val: Current value of the lock > >> + * @node: Pointer to the MCS node of the lock holder > >> + * > >> + * *,*,* -> 0,0,1 > >> + */ > >> +static __always_inline bool __set_locked_empty_mcs(struct qspinlock *lock, > >> + u32 val, > >> + struct mcs_spinlock *node) > >> +{ > >> + return atomic_try_cmpxchg_relaxed(&lock->val, &val, _Q_LOCKED_VAL); > >> +} > > > > That name is nonsense. It should be something like: > > > > static __always_inline bool __try_clear_tail(…) > > We already have set_locked(), so I was trying to convey the fact that we are > doing the same here, but only when the MCS chain is empty. > > I can use __try_clear_tail() instead. Thing is, we go into this function with: *,0,1 and are trying to obtain 0,0,1. IOW, we're trying to clear the tail, while preserving pending and locked.