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From:   =?utf-8?Q?Javier_Gonz=C3=A1lez?= <javier@javigon.com>
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Subject: Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold
Date:   Mon, 4 Feb 2019 09:14:10 +0100
In-Reply-To: <CANr-nt0FWrzsCmv=X8oqCSOBYTO7nZi5gtKJN13setFQ8MFjRg@mail.gmail.com>
Cc:     =?utf-8?Q?Matias_Bj=C3=B8rling?= <mb@lightnvm.io>,
        Hans Holmberg <hans.holmberg@cnexlabs.com>,
        linux-block@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To:     Hans Holmberg <hans@owltronix.com>
References: <20190130102604.14496-1-javier@javigon.com>
 <CANr-nt27moc9eLMgXkoXQGR7GA=uRpg2u+v7aJxzNB_AGbw5hQ@mail.gmail.com>
 <E4DF0FFC-5A45-405D-A942-DD8572CC1BD1@javigon.com>
 <CANr-nt0FWrzsCmv=X8oqCSOBYTO7nZi5gtKJN13setFQ8MFjRg@mail.gmail.com>
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> On 31 Jan 2019, at 21.10, Hans Holmberg <hans@owltronix.com> wrote:
>=20
> On Thu, Jan 31, 2019 at 5:33 PM Javier Gonz=C3=A1lez =
<javier@javigon.com> wrote:
>>> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@owltronix.com> wrote:
>>>=20
>>> Hi Javier!
>>>=20
>>> How did you test this? I'm trying to add a test case to our testing =
framework.
>>>=20
>>> This is what i ran in qemu, and I got a hang (with this version of =
the patch)
>>>=20
>>> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
>>=20
>> I run several low configurations without problem. Can you share the =
qemu configuration and version?
>=20
> Of course!
>=20
> qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
> branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)
>=20
> My geometry:
> parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
> 24, cunits=3D0

You are right, lmw_cunits=3D0 gives the problem.

What about the following? If it goes through cijoe, I'll send a V3.

diff --git a/drivers/lightnvm/pblk-rb.c b/drivers/lightnvm/pblk-rb.c
index d4ca8c64ee0f..a6133b50ed9c 100644
--- a/drivers/lightnvm/pblk-rb.c
+++ b/drivers/lightnvm/pblk-rb.c
@@ -45,10 +45,23 @@ void pblk_rb_free(struct pblk_rb *rb)
 /*
  * pblk_rb_calculate_size -- calculate the size of the write buffer
  */
-static unsigned int pblk_rb_calculate_size(unsigned int nr_entries)
+static unsigned int pblk_rb_calculate_size(unsigned int nr_entries,
+					   unsigned int threshold)
 {
-	/* Alloc a write buffer that can at least fit 128 entries */
-	return (1 << max(get_count_order(nr_entries), 7));
+	unsigned int thr_sz =3D 1 << (get_count_order(threshold + =
NVM_MAX_VLBA));
+	unsigned int max_sz =3D max(thr_sz, nr_entries);
+	unsigned int max_io;
+
+	/* Alloc a write buffer that can (i) fit at least two split bios
+	 * (considering max I/O size NVM_MAX_VLBA, and (ii) guarantee =
that the
+	 * threshold will be respected
+	 */
+	max_io =3D (1 << max((int)(get_count_order(max_sz)),
+				(int)(get_count_order(NVM_MAX_VLBA << =
1))));
+	if ((threshold + NVM_MAX_VLBA) >=3D max_io)
+		max_io <<=3D 1;
+
+	return max_io;
 }

 /*
@@ -67,12 +80,12 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int =
size, unsigned int threshold,
 	unsigned int alloc_order, order, iter;
 	unsigned int nr_entries;

-	nr_entries =3D pblk_rb_calculate_size(size);
+	nr_entries =3D pblk_rb_calculate_size(size, threshold);
 	entries =3D vzalloc(array_size(nr_entries, sizeof(struct =
pblk_rb_entry)));
 	if (!entries)
 		return -ENOMEM;

-	power_size =3D get_count_order(size);
+	power_size =3D get_count_order(nr_entries);
 	power_seg_sz =3D get_count_order(seg_size);

 	down_write(&pblk_rb_lock);
@@ -149,7 +162,7 @@ int pblk_rb_init(struct pblk_rb *rb, unsigned int =
size, unsigned int threshold,
 	 * Initialize rate-limiter, which controls access to the write =
buffer
 	 * by user and GC I/O
 	 */
-	pblk_rl_init(&pblk->rl, rb->nr_entries);
+	pblk_rl_init(&pblk->rl, rb->nr_entries, threshold);

 	return 0;
 }
diff --git a/drivers/lightnvm/pblk-rl.c b/drivers/lightnvm/pblk-rl.c
index 76116d5f78e4..b014957dde0b 100644
--- a/drivers/lightnvm/pblk-rl.c
+++ b/drivers/lightnvm/pblk-rl.c
@@ -207,7 +207,7 @@ void pblk_rl_free(struct pblk_rl *rl)
 	del_timer(&rl->u_timer);
 }

-void pblk_rl_init(struct pblk_rl *rl, int budget)
+void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold)
 {
 	struct pblk *pblk =3D container_of(rl, struct pblk, rl);
 	struct nvm_tgt_dev *dev =3D pblk->dev;
@@ -217,7 +217,6 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
 	int sec_meta, blk_meta;
 	unsigned int rb_windows;

-
 	/* Consider sectors used for metadata */
 	sec_meta =3D (lm->smeta_sec + lm->emeta_sec[0]) * =
l_mg->nr_free_lines;
 	blk_meta =3D DIV_ROUND_UP(sec_meta, geo->clba);
@@ -234,7 +233,7 @@ void pblk_rl_init(struct pblk_rl *rl, int budget)
 	/* To start with, all buffer is available to user I/O writers */
 	rl->rb_budget =3D budget;
 	rl->rb_user_max =3D budget;
-	rl->rb_max_io =3D budget >> 1;
+	rl->rb_max_io =3D threshold ? (budget - threshold) : (budget - =
1);
 	rl->rb_gc_max =3D 0;
 	rl->rb_state =3D PBLK_RL_HIGH;

diff --git a/drivers/lightnvm/pblk.h b/drivers/lightnvm/pblk.h
index 72ae8755764e..a6386d5acd73 100644
--- a/drivers/lightnvm/pblk.h
+++ b/drivers/lightnvm/pblk.h
@@ -924,7 +924,7 @@ int pblk_gc_sysfs_force(struct pblk *pblk, int =
force);
 /*
  * pblk rate limiter
  */
-void pblk_rl_init(struct pblk_rl *rl, int budget);
+void pblk_rl_init(struct pblk_rl *rl, int budget, int threshold);
 void pblk_rl_free(struct pblk_rl *rl);
 void pblk_rl_update_rates(struct pblk_rl *rl);
 int pblk_rl_high_thrs(struct pblk_rl *rl);
--
2.17.1


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