linux-kernel - Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold

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Date:   Mon, 4 Feb 2019 09:14:10 +0100
From:   Javier González <javier@...igon.com>
To:     Hans Holmberg <hans@...tronix.com>
Cc:     Matias Bjørling <mb@...htnvm.io>,
        Hans Holmberg <hans.holmberg@...xlabs.com>,
        linux-block@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2] lightnvm: pblk: prevent stall due to wb threshold


> On 31 Jan 2019, at 21.10, Hans Holmberg <hans@...tronix.com> wrote:
> 
> On Thu, Jan 31, 2019 at 5:33 PM Javier González <javier@...igon.com> wrote:
>>> On 31 Jan 2019, at 11.41, Hans Holmberg <hans@...tronix.com> wrote:
>>> 
>>> Hi Javier!
>>> 
>>> How did you test this? I'm trying to add a test case to our testing framework.
>>> 
>>> This is what i ran in qemu, and I got a hang (with this version of the patch)
>>> 
>>> nvme lnvm create -d nvme0n1 -t pblk -n pblk0 -f -b 0 -e 0
>> 
>> I run several low configurations without problem. Can you share the qemu configuration and version?
> 
> Of course!
> 
> qemu remote: https://github.com/CNEX-Labs/qemu-nvme.git
> branch: master (cb200e3ccf9c1ff21f6275c6cb68b2801135a640)
> 
> My geometry:
> parallel units: 8, secs per chk: 768, meta size 16, ws min 12, ws opt
> 24, cunits=0

You are right, lmw_cunits=0 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 = 1 << (get_count_order(threshold + NVM_MAX_VLBA));
+	unsigned int max_sz = 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 = (1 << max((int)(get_count_order(max_sz)),
+				(int)(get_count_order(NVM_MAX_VLBA << 1))));
+	if ((threshold + NVM_MAX_VLBA) >= max_io)
+		max_io <<= 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 = pblk_rb_calculate_size(size);
+	nr_entries = pblk_rb_calculate_size(size, threshold);
 	entries = vzalloc(array_size(nr_entries, sizeof(struct pblk_rb_entry)));
 	if (!entries)
 		return -ENOMEM;

-	power_size = get_count_order(size);
+	power_size = get_count_order(nr_entries);
 	power_seg_sz = 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 = container_of(rl, struct pblk, rl);
 	struct nvm_tgt_dev *dev = 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 = (lm->smeta_sec + lm->emeta_sec[0]) * l_mg->nr_free_lines;
 	blk_meta = 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 = budget;
 	rl->rb_user_max = budget;
-	rl->rb_max_io = budget >> 1;
+	rl->rb_max_io = threshold ? (budget - threshold) : (budget - 1);
 	rl->rb_gc_max = 0;
 	rl->rb_state = 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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